Gear noise/whine on '99 C4?

I searched on this topic and did not find anything... I have a 1999 Carrera 4 with 156,000 km on the odometer. I have only owned it for 3 months, so am still learning. Despite the high mileage, the car looks good, has lots of power and is tight and solid on rough roads. When driving at normal highway speeds, say 60-75 MPH, there is a very noticeable gear noise, coming from the back. (not from the AWD stuff in the front end). I have analyzed this closely and am sure that: (1) it is not tire noise (2) it is not engine noise It happens in both 5th and 6th gears. Suppose I am driving on a level road at a constant speed of, say 70 MPH. There is just enough throttle down to maintain this speed. Now, I can hear tire noise, wind noise, etc. Then, I apply a light load, by opening the throttle just a little. A very noticable gear noise is heard. It is not a high pitch whine, more like a lower frequency humming. When I ease off on the accelerator, the noise goes away. The noise occurs under very light loading, (and higher loading too). It may happen in the lower gears but seems to be most noticable in 5th and 6th, on the highway. Should I be worried? This is the only 996 I have driven. I know that some gear noise is inherent with all manual transmission cars, but this condition is much noisier than other manual tranny cars I have owned. ....Rickker '99 C4

I have the same year c4. Yes there is a gear whining noise from the tranny in 6th that changes with rpms. No worries on my part. I'll only worry when I change my tranny fluid and see shiny flakes pouring out. My friend has the same noise in his c2.

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Thanks, springgeyser. That's some comfort to me. I can handle the noise, as long as it doesn't mean the transmission is going to pack it in. I am surprised, if this condition is typical of '99 C4s, that Porsche would have gone into production with a drive train prone to be noisy under load. Maybe this was engineered out of the newer models? ...Rickker

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I had the same noise in my 1999 C2 starting around 85,000 miles. At first I thought it was just tire noise. I was covered by a CPO warranty so I took it into the dealer and they disagnosed it as bad bearings in the serpetine belt pulleys. But that did not cure it and it got louder as time went on. It was most noticeable when giving it throttle in 5th or 6th. Back off the throttle and the sound almost went away. Took it back in for the 90,000 service and had them look for it again. They thought it was the alternator this time and replaced that but the sound was still there. So they opened up the transmission and found that the clutches on the limited limited slip were shot. The giveaway was that the inside of the transmission was black with gunk from the clutches. As a result I got a new transmission under waranty. Other than the noise there was nothing to indicate any problems. The car drove and shifted just fine. I probably didn't really have limited slip but it never caused me any problems. It took a very determined service manager to find the problem and then he had to fight with Porsche to get them to just replace the transmission. They only wanted to replace parts but the price differential was only a couple of hundred dollars. I hate to say it but your description matches what I experienced. The service manager did tell me that if I could have tolerated the noise I could probably have driven the car for many more miles without any problem but since it was under warranty replacement was the answer. You might want to change the transmission fluid and see what it looks like. If you get black gunk out, you might have your answer.

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That may very well be the answer, sigh.... I know that I was just kidding myself that such noise could be "normal". I think your advice on draining and closely looking at the transmission fluid is the way to go. If it is clean, then I would feel better about driving the car for a while before having the transmission removed and reconditioned. One thing puzzles me. Your noise characteristics were the same as mine, and when the shop open up your transmission, they found the limited slip clutches worn out. It would seem to me that such clutches would not be engaged or activated when cruising at a steady speed in 5th or 6th. So why would they be noisy? Puzzling. Thanks for your reply, even though it was not what I wanted to hear. ....Rickker

I've got an 01 C4 and I really don't notice any kind of gear noise on the highway. Certainly wind and road noise, but not gear noise. I'd have it looked into personally. At least start with a transmission fluid swap and see if that either helps the noise or shows you anything in the drained fluid.

I get gear whine of some sort when I'm off throttle at those speeds and gears... but not when I'm applying throttle.

I had some gear noises. Turns out there were holes in my bellhousing where the pressure plate screws had broken off and went through.

The fact the differential is part of the trans makes it hard to pinpoint where a whine originates. You probably would have to open both and spin each component by hand to see if there is a bad bearing or if there is excessive/loose backlash of the mating gears.

Bump... Pardon the n00b repost... this is a repost of a post I made in the wrong forum (944) a few minutes ago I'm interested if this noise problem was ever solved? I have a similar noise when applying the accelerator gently from coasting to accelerating. It is almost like a scraping sound too. I had my '00 996 Carrera 2 at a Speed shop yesterday and my mechanic thought the sound was coming from the axel bearings by the differential. I do not hear the noise if in neutral while coasting at any speed or when revving the engine without the transmission in gear. The noise is more pronounced when in a high gear (i.e. 5th) and driving at 50mph. The noise occurs only after/while applying the accelerator from a coasting in gear. Any help is greatly appreciated. Best regards, Markus

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I am having this EXACT same problem with a 2000 911 C2 that I am looking into buying. I was curious if you could tell me what precisely I would have to replace part-wise if I did not want to replace the whole transmission or differential. I am getting a good price on the car and only want to buy it if I can fix this issue.

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Constant whine for me were the Tranny bearings (rebuilt the tranny). I also had another whine that occured depending on whether I was cornering which turned out to be the wheel bearing (replaced the wheel bearing $700).