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!

 

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.

 

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.

 

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 :-)

 

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.

 

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