'01 with 67K and basically stock except Comptech cat-back and AEM CAI.

The car has always seemed to make a little rear-end noise when you hover between accelrating and decelerating at slow speeds, but a while ago it started making a new noise which is constant and does not change in pitch, tone or volume with any driver inputs. The new sound is definitely from the output of the transmission back (While rolling about 30MPH I put it in neutral, shut the engine off and let out the clutch to verify it was nothing forward of the tranny) and seems to be coming from under the car with the top up. The sound is hard to describe and harder to capture on audio. Best words; it's a whirring noise that is directly proportional to the speed of the car. Again, it does not change in turns, acceleration, deceleration or braking. Aside from the few bolt-ons, the only changes were tires and brakes and the sound started before the brakes were done and continues now. Temp does not seem to have an effect either.

 

does it make the sound when you push in the clutch? the throw out bearing can cause a weird noise.

 

almost sounds like a bad rear end.... but that's without actually hearing the noise

 

Clutch has no effect. That was my first thought, but I think I eliminated anything forward of the tranny output shaft by shutting it off while doing about 35MPH, shifting into neutral and letting out the clutch (the stopped engine should keep everything forward of the tranny from rotating).
It almost sounds like there's no oil in the rear end or tranny but I have changed both. The old oil looked like it was brand new (or at least, golden without any signs of debris or darkening).

 

Maybe tranny bearings or diff going....