Now what?s this (squealing) noise (at 3000 rpm)???

Short summary: The car (a 3.6 liter 996.2) started making a rasping/metallic sounding noise at around 3000 to 3100 rpm, at least when the engine wasn�t 100% warmed up. So I took it in to have it checked. They replaced a belt to the rear of the engine (photo below). No more metallic/rasping noise at 3000. But now a squealing noise at 3000 :-((. I�ll post more details in a second post, and a video as soon as I can. But I will soon take the car to have it checked again, and I�d hugely appreciate any advice what to look for (no one near me is terribly experienced with 996s). I�d also appreciate advice re. whether it�s a mistake to drive the car until this is diagnosed/fixed � . Thanks!!!

Further details: While the first noise seemed to only occur in or very very close to the 3000 to 3100 band, the second one seems to occur at more engine speeds, though it is worst around 3000. I definitely also heard it as the revs dropped from somewhere in the 2500 to 3000 range to 2000 or lower. I somehow associate squealing noises in other cars with power steering and air conditioning, and the a/c was turned on for the first time this year by the people who replaced the belt, and I turned it back on for a second time before completing my drive home. But I’m not sure it was ever on when I heard the noise, and it was definitely off some times when I heard the noise. Both noises are/were most noticeable when the car is sitting in neutral. Indeed, I don’t remember if I heard either noise while moving, though I do remember thinking, while driving with the windows down “isn’t that it?” (the first noise, before the belt was changed). Also, the first noise may not have occured when the car had been at operating temperature for a while – at least once the noise disappeared in such a case. And the second seems not to occur when the car is completely cold, but does occur when it’s partly warmed up (haven’t tested it fully warmed up). I described the first noise as rasping, though I’m not 100% sure what this means. Given the sound, I supposed it could be a loose exhaust tip, or one exhaust pipe vibrating against another. But these things seem pretty securely in place. Thanks again for any help with this!

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The bearing in your water pump can do this. When was the last time you replaced the water pump and how many miles do you have on your car?

Hi rs10, It sounds like you had the serpentine belt replaced. It ties together all of the auxiliary units (a/c, power steering, alternator) to the engine drive it also connects the water pump and has several idler wheels. A new belt can make some noise when it is first installed if they don't dress it. But, more likely as the new belt will be slightly tighter, it is bringing out another issue. It is possible that it is just a dirty idler but the only way to tell for sure is to remove the belt and move all of the wheels the belt goes over by hand. It could very easily be a bearing that is going bad and the new belt is making it more evident because the belt is tighter. The most likely bearing would be the one in the water pump as they are a known wear item. Removing the belt is not complicated, really not a lot harder than changing the air filter so if you are comfortable with that kind of maintenance you could check it yourself. If you want to tackle it there are a number of good threads on here about it and I'm sure lots of RLers would be glad to help walk you through it. You do want to check it right away. A bad water pump can be very bad for your engine if it starts to break up. Does the pitch of the noise change with RPM?

For more ideas suggest you check out the Pelican diy for idler pulley replacement. http://www.pelicanparts.com/techarti...Tensioners.htm

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Thanks tharbin, nailedit, and Schnell Gelb for the very helpful advice!!! Not sure it's ever been replaced. The car has under 50k miles according to the odometer, though it's not impossible it has more. Given the history, I can't imagine it has more than 70 or 80. Yes, I'm pretty sure that's it. See the photo. I'm told the belt manufacturer (it's hard to read the brand name - probably Conntech) is (one of) the best. Hope that's right. (Sorry the photo is sideways. That's not how it looked on my screen, nor on my smart phone. Sorry it's so annoyingly big too - but I haven't found anything I can do about it.) Dress means lubricate? Idler means wheel? Or pulley? Or ... ? I have not noticed. If I raise the revs to 3k or further and then lift off, the squeal does trail off, but whether that's a change in pitch or just a change in volume, I'm not sure. Alas, I'm not sure whether its due to crappy speakers on my computer, or a crappy smart phone, but in the videos I took, I can't hear what I heard in the car. A sound change at 3k yes. But can I recognize it as a rasp or a squeal, much less know whether the pitch changes, no. (Due to this, and the extra complication of uploading video compared to a photo (seems I'd need to remember my YouTube user name or create a new one), while I tried to upload a video today, I won't manage. Maybe Friday/this weekend.) Thanks again!

That is the serpentine belt. Yes belt dressing is a lubricant but it is not recommended for modern belts. Some mechanics still use it as it will quiet a belt temporarily but with modern belts it can actually cause problems down the road. Only reason I mentioned it was that if it was dressed it would almost certainly not be the belt making the noise. If you look at the picture you uploaded you can see two black wheels. There are three black wheels near each other. They are idlers because they do not drive other components (e.g. alternator). The two to the left just guide the belt and the one to the right is the tensioner. It is connected to a spring mechanism that applies the tension to keep the belt tight. Much better than the old days of adjusting the alternator position to get belt tension. A trick you can use to quickly eliminate them is to spray a little WD-40 or similar on the bolt for the idlers. If the sound goes away that is the problem. Sometimes that will actually be enough to fix it. You can also try spraying WD-40 behind the pulley, onto the bearing for the A/C compressor and alternator to see if it goes away. I've heard that the trick also works for the water pump but have never tried it. If it is the water pump bearing, replace the water pump right away even if the sound goes away. If the impeller starts to wobble on the water pump from a worn bearing, little bits of the impeller can shear off and get into the engine's water passages possibly causing hot spots which will most likely damage the engine.

A bit of an update: I drove the car to have it looked at by the guys who replaced the belt and then back home, and not a squeal from the engine. A bit of roughness between 3000 and 3100 when the car was cold, little or none (hard to be 100% sure) when warm. They told me the water pump was the first thing they looked at, and that it's fine. A bit surprising. After the first day when I heard the squeal, I did go back a day later, start the car up, and drive it around a few times to be sure the squeal was not a one-off thing. Maybe it was a "two-off" thing. Maybe the belt just takes time to get bedded in, or something like that? On the other hand, I've heard harshness at 3000 on start up at least once or twice before, a year ago. And there was one mechanic/Porsche specialist who told me at the time that he consistently heard something wrong at 3000. But I was not convinced and got several second opinions, including from the Porsche dealer, and they all told me there is no problem ... .

Since the new belt is tighter, the pulleys and accessories are also under slightly more tension than before...especially if the tensioner has relaxed with age. If there was any play in the water pump bearing beforehand, the new belt could have caused the the impeller vanes to interfere with the block - at least until the interfering edges of the vanes were machined away against the block. Even though your garage assured you that the water pump is fine, take the 5 minutes to use a socket and breaker bar to relax the belt tensioner and try to wiggle the water pump pulley back and forth. If you feel any lateral play, replace the pump. The new squeal could also have been something benign - maybe the mechanic got some grease on the grooved side of the new belt - but checking the water pump is simple to do and expensive to ignore.

I will have to have the water pump pulley checked as suggested - next week, as it isn't something I could do myself this weekend. In the meantime I drove the car again today, and all was fine. Then as I neared home I thought I heard some high pitched sound while driving with the windows down. Seemed to come from the right rear (though perhaps it seemed to come from the right because it was bouncing off of parked cars and walls, whereas there was nothing so close to bounce off of on the left). So after parking, I revved the engine to see what happened around 3k. No rasp and no squeal. But a bit of a screech, even with windows closed :-( . Not so loud as the previous rasp and squeal. And it actually started closer to 2900 and continued above 3000. (I don't remember exactly how far above 3000, except that by 3100 it was definitely gone.) There was a bit of a flaw in my test procedure, by the way: Once I parked, I stopped the engine, then remembered I wanted to do this test and immediately restarted it. And there was more of a screech the first time I revved the engine than the second. So I have to wonder if the result would have been different had I simply left the engine on. I think the engine was at or near normal temperature, but I'm not sure. The water temp was around 75 C / 170 F, so below normal. But I had only driven the car for a few minutes after it had sat for an hour cooling down from a longer drive. So I expect the oil and other parts of the engine were warmer than they usually would be when the water is around 75 / 170. Just when I was hoping I could just drive the thing and stop worrying ... .

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You said the shop checked the water pump and it was fine. Unless you have reason to not trust them I would go with your last comment. Just drive it and stop worrying. If we obsessed over other cars the way we do over 996s nobody would ever get to work. Cars make noises, they click, pop, squeal, whine, fart, gurgle, scream and just about every other imaginable sound from time to time. Most of them, including 996s, recover and continue on their merry way. Now, that said, if it gets worse, have it checked again.

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My experience is a serpentine belt should *not* make any noise except possibly after a wash during which the belt got wet. It might chirp or lightly squeal upon engine start until the water dries. If the old belt was shredded you have to consider an idler/tenionsioner roller bearing is going bad and dragging. If the old belt had worn/sharp edges this is a sign the belt is not tracking properly and this can be a sign an accessory drive is failing, developing too much bearing play and the pulley gets out of position and the belt rubs. The most common accessory drive to fail is the water pump. A careful check of the play of all the accessory drives can identify the bad one. Hopefully the shop that replaced the belt knows all of the above (and a lot more besides) and eliminated a worn accessory drive or idler/tensioner roller bearing. The noise suggests to me not a belt problem though but possibly an AOS problem. While replacing one of these is not the biggest repair bill it is not something one wants to do unless truely called for. But to know the AOS has to be clearly identified or eliminated as the source of the noise and engine behavior.

Thanks everyone for all the helpful advice! After following up on all this with the people who put in the new belt, still no clear answer, so I went to the Porsche dealer. They are quite confident it's the oil pump. They say they saw this once before on a car with far more miles (and a much louder noise). Bad news: very hard (expensive) to replace. Good news: no need to do it now. Maybe never, unless/until I can't live with the noise. Apparently the pump is functioning quite well, providing plenty of pressure. I asked if there would be any reason to worry that the oil pump might not do it's job during a track day, and they said no. (Which I understand to mean there is no reason to worry it would not do it's job in a situation when a new oil pump would ... .) Both the original guys and the Porsche dealer confirmed that everything attached to the serpentine belt is OK. (I forgot to tell the Porsche dealer not to start there ... .)

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Yes, I was thinking pretty much the same thing recently. The car I drive to work has more squeaks and rattles than my 996, yet somehow they almost never bother me, whereas anything on the Porsche has me hunting for a solution. On the other hand, if it's a Porsche and it's an engine noise, I guess it's better to know.

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Well, that's a new one on me. First time I've come across a report the 996 engine oil pump can make a noise loud enough to be heard over other normal engine/car/road noises.

Does sound a bit strange, doesn't it. Maybe it's the belt (chain?) that drives the pump? Or a defect in the wheel on the pump which the belt/chain turns makes the belt/chain make noise? None of these things sound terribly good ...

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Where are you located I may have a solution.

Oh my! Thank you Nailedit for providing some assistance to rs10. No offense but you really need some better understanding of your engine. No, the serpentine belt has nothing to do with the oil pump. If in fact the correct diagnosis is the oil pump, stop driving the car and get it fixed! It is not really all that expensive relatively speaking but if it is making ANY squealing noise then something is drastically wrong. You do not want any problems with your oil pump and you should not wait to get this critical component repaired. Oil pump diagram: http://www.autoatlanta.com/porsche-p...section=104-00 And so did you watch them check everything running from the serpentine belt? They of course removed the air filter box, removed the serpentine belt, and by hand moved every idler pulley, water pump, alternator pulley, power steering pump and so on? By hand, checking for any play or roughness in turning? You saw them do this?