Differential, wheel bearings, gearbox?

First off, I will try to get my phone to record the noise if possible. Second, I have done some research, and yet, I am still posting. 2002 996.2 with about 87k miles. Daily driven, city about 2/3, and longer highway 1/3 of the time. I drive it hard 50% of the time. Had IMS, new clutch, and some other bits and bobs about 15k ago. I have a noise coming from what sounds like the rear of the car when cold. Sounds mechanical, like gears interacting with each other. Alternatively, it sounds almost like there is something sticky on the tires in one spot of the contact patch and every time the tire rotates past that spot, it sounds like a sticker being pulled off. If that makes sense. It only happens when the car is cold, or before it has been driven to operating. I hear it only when windows are down and there is something for the noise to be reverberated off, like parked cars or a wall or something. Furthermore, it only makes noise when the car is moving. So it is not internal mechanical, i.e., not associated with the motor or RPM's. I have heard some tires start to make sounds like this when they get to a certain age, so I am hoping that is all that it is. I run 36-40psi in the rears. It appears to be unassociated with tire pressure. In my mind, sounds like a differential. Once the oil heats up, the sound goes away (again, in my head that is what it seems/sounds like). I know diff problems are rare. I also thought it could be gearbox and the fluid needs replacing. In the end, I will try to get video of the noise and post that. Thanks!

Hello all, I just took my 11 997.2 tts out for a drive and noticed that during deceleration there is a very noticeable whining sound from what sounds like the rear of the car, however it's difficult to be sure. I let the fluids warm up but the sound is still present. Oil level is good, no codes, and the car seems to drive fine otherwise in all modes. The only mods are muffler delete and springs. I have also ruled out tire noise. I have seen a few forum post on the matter, but I failed at finding anything specific to the 997tts. The nearest Porsche dealer is 200 miles away, so I am reluctant to drive the car down there. Any thoughts or suggestions? Thanks!

Jack it up so you can rotate the wheel and see if you can hear it then. I had a brake dust shield do something similar, it made an odd rhythmic sound and I could only hear it with the window down. Just took some adjusting for clearance. Hope yours will be that simple.

Quotes source post: 4563036

Quote: I take it the whine is new? Both of my cars emit a bit of tranny/diff whine but not enough to worry about. Unless it is obvious to you the noise is not normal you might have to enlist the ears of someone in town who has some good knowledge of what healthy and sick transmissions/diffs sound like even if he is not able to repair the Porsche transmission/diff if it proves sick. If he says it is "sick" then you are looking at a flat bed trip to the dealer to have this looked into. The noise might be a wheel bearing, or even tire noise. I do not know how you can rule out tire noise. My 996 Turbo had a whine at speed that had my suspecting wheel bearing and I took the car to handy -- well 140 miles away -- dealer (in OKC) and the tech there checked the car over and told me the noise was from the front tires. He showed me -- had me feel actually -- the tread blocks of the front tires and sure enough I could feel the feathering and see the scrubbing take place. A drive home nearly 1500 miles away and an alignment had the noise gone after driving some more and scrubbing the tires in to the new alignment. Also, my experience is worn tires can generate some considerable noise. Anyhow, is the noise present in all gears or at least a couple of the higher gears? If you put the tranny in neutral does this affect the noise? If a manual transmission if you press on the clutch does this affect the noise?

Yes, I have thought about this as well. I will definitely take a look at the dust plates. But, it just seems strange to go away after time on the road. I will update this as I go along.

I have had a wheel bearing do that before!

The diff and tranny share gear lube. Drain a bit of the oil and see what you get. My '99 C4 had a noise related to road speed. I hoped it was the all wheel drive. Cold vs warm was not much different. In my case there was a lot of fine metal :-( when I pulled a sample. I put off the rebuild and had to spend an extra $1500 on a used ring gear and pinion shaft. The movement of the ring gear because a diff bearing failed galled both beyond use. I think I know why the PO traded the car in. The rebuild was worth it. I've put 115,000 on it since the rebuild :-)

Yes, the whining sound is new, and very noticeable. I had driven the car three days prior and didn't notice it then. I suppose it's possible that the whining sound was present at that time, but I'm one of those guys that typically notices if anything is "off" each time I drive the car. I finally had some time to get back to this and with the help of a friend. I have found that the "whining" occurs in all gears. Furthermore, the pitch and tone changes with the speed of the car and not with the RPM's. I put the car in neutral at speed and the sound remains. There doesn't seem to be any change whilst driving in reverse or going around corners. I started to second guess my statement about ruling out tire noise, but the sound occurs on different surfaces e.g. blacktop, concrete, etc. I'm no mechanic, but it does sound mechanical in nature. The dealership is picking the car up this week. We will know soon enough where the sound is coming from. Thanks for the input!

Okay, pretty sure I have narrowed it down to tires. I have heard of this before from other 911 owners. I checked rears off the car, and the inside shoulders are basically bald, and the rest of tire is manageable. I knew tires were upcoming. The sound comes from rotational movement, no question. I will buy some rears and see what changes, if anything. Will update this.

Update - After an extensive inspection and tests with sound equipment, it was first discovered that the bolt holding the left side lower control arm to the body of the car was very loose. This was detected when checking for play in the bearing. This loose bolt allowed nearly 1/3-1/2 inch of play left to right. This hub movement translated to movement with the left front half shaft, which in turn put stress on the gears inside the differential causing them to wear aggressively. Through the use of Chassis Ear sound diagnostic equipment we isolated this sound to the gearbox. It was also discovered that fluid seepage was all over the left side output of the differential when it had flung gear oil while this output flange was being pulled and pushed. A new diff and will be installed. Hopefully this information is useful.

Figured this out. Turned out to be low pressure in tires(also at the end of their life). Rears to be exact.

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Quote: Thanks for the update. Wonder how that bolt came to be loose? Just bad luck I guess.

Quotes source post: 4570316

Quote: I suspect we'll never know. Bolts come loose all the time, right? But.............I am told, however, that the bolt in question must be replaced with a new one once removed. When I bought the car (CPO'd) it had GMG springs, and unknown to me until now GMG bushings. Perhaps I should have been more thorough with my inspection and not relied on the CPO alone before purchasing this car. Lesson learned! It has been explained to me that to install springs and bushings this bolt must be removed, and therefore any warranty claim would be declined due to outside influence. I'm not privy to the internal discussions (PCNA & dealership) that ensued, but the dealership that certified the car is repairing the car at no cost to me. I'm no expert, but from reading other stories regarding aftermarket parts, it seems Porsche would have a hard time proving the springs and/or bushings lead to the diff failing. I am very thankful to the dealership to say the least. I kept these details to myself while working towards a resolution, as not to inflame the situation should anyone from the dealership read the forums. Now you know.