Odd Engine Noise

I have a 2003 C2 with roughly 40K miles - oil changed annually and fluid levels are fine...no leaks. Overall, the car has been very reliable and run well...so far. The engine recently started making an odd noise. I thought I would run this by you all to get your thoughts on what the cause might be realizing it ist difficult to diagnose these kinds of things remotely. I tried to record the noise, but it doesn't capture well. I've run a search, but haven't found anything like this...the posts I've seen have been mostly lifters, SAI, etc. As best I can describe the noise, it sounds like a refrigerator when the compressor is going bad...like something is out of round. It is not a ticking sound, so I'm suspecting a bearing of some kind is going - yes, I replaced the IXX when I bought the car - it doesn't sound like ticking or clacking. The sound does not occur at start-up, and I start to hear it once the car has reached operating temperature. When the engine revs to ~1,500, the sound disappears, although the noise does seem to change pitch as the revs increase. I can hear it best in the cabin, but the engine noise seems to drown it out when I open the decklid. It does not go away when I depress the clutch. I've checked around the various pulleys, etc. and none seem to have any play, but I'm not ruling them out. My initial thought was the water pump getting ready to go, but the indicators I've read on Rennlist don't seem to be present here. Apologies for the long post, just want to provide as much information as possible. Any thoughts would be much appreciated.

Have you checked whether the sound is coming from the alternator? Try turning large electrical loads on and off to see if the sound changes. You can use the old "listening stick" device and put a wooden dowel on various parts of the engine, alternator, waterpump, etc. and put the other end close to your ear and listen. Obviously be very careful of where you put a stick into a running engine compartment!

Mine was making some kind of scrapping noise. Above 1500rpm, I can't hear it because engine is louder. Water pump was new. I took the belt out and the noise stopped. Turned out to be alternator shaft was bent and making that scrapping noise.

"I can hear it best in the cabin, but the engine noise seems to drown it out when I open the decklid. It does not go away when I depress the clutch." It seems to me, that this would indicate that the noise is coming from the "front" part of the engine (the end that's attached to the transmission).

Remove serpentine belt, check all pulleys for play...spin them by hand and see if any exhibit play or make a grinding noise, check alternator for play and noise, check power steering pump, check water pump for play and noise. I would inspect the water pump closely, could be your source since as the coolant heats up it gets warmer and bearings expand enough to have some play.

Regardless, an 03 911 is living on borrowed time with an original water pump. Time to replace with a new OE Porsche, gasket, thermostat, and coolant flush.

Quotes source post: 12083848

In these cases I always advise the car be taken to a tech pronto for a professional diagnosis. When in doubt I prefer to flat bed the car, too, just to avoid the risk of something happening on the way to the shop. Based on what you wrote my guess would be water pump. If you want to get your hands dirty with the engine cold remove the serpentine belt. Beforehand you must note the proper belt routing. Draw a picture/diagram, take photo. Also, if you are not going to replace the belt but reuse it note the direction of rotation so you can install the belt so it rotates the same way as before. With the belt out check for any sharp edges. A sharp edge is sign the belt is rubbing and this arises from an accessory drive developing bearing play that allows the pulley to be moved out of proper alignment. Check each accessory drive for any play. You have a number of these to use as reference. If one is bad, has too much play, you'll know it from comparing the play (or lack of play) of all the accessory drives. A close examination around the water pump, behind/underneath the pulley for any signs of a fluid leak is called for too. If you find the water pump (or another accessory drive) with what you believe is an excessive amount of play button everything up and flat bed the car to a dealer service department/indy shop for a professional's diagnosis and repair. If you find no excessive play button everything up and flat bed the car to a dealer service department /indy shop for a professional's diagnosis and repair.

Thanks all for the input. The comments were helpful and confirm my initial suspicions. Rather than pretend I know what I'm doing, I've taken the car into my indy to look over. Hopefully, I caught the problem early and I'll be back on the road before too long. Once I hear back, I'll let you know what the issue was.