Ok guys/gals, got one for you. Have a humming/ droning noise coming from center front area of car. Noise is only apparent from 38mph to about 60-65mph then fades out; starts out at its loudest sound at lower speeds progressively fading out as the speed increases. Definitely drivetrain related as noise is not effected by engagment of transmission or engine; I can coast at that speed in neutral and get the same results. Noise consistently increases in pitch but remains constant through gear changes. I don't think it is wheel bearing related as I already replaced two and are pretty aware of the sound and it's association with turning, however I have not physically checked them yet. Car just turned 100k.

Is there any typical components in the drivetrain (ie. universal joints, diff. bearings)that would normally cause this noise and become prone to failure at high mileage? Trying to get a feel on what may be suspect before taking it anywhere for a "professional" diagnosis. I would definitely do the work myself. Anly help would be appreciated, thanks again guys.

 

Did you ever figure out what the issue was?

I have the same exact noise with my 2.8 Q. It started around 100k miles and I now have 103k. I personally replaced all 4 wheel bearings and the noise is still present but not as bad.
It starts at 20mph and fades out by 25mph.

This has me baffled and it's driving me nuts.

 

I found the solution to my problem.

I've found the noise was associated to the tires. There was some cupping and uneven tire wear. This uneven ware hitting the surface of the road caused the humming/grinding, or knobby noise as I refer to it.
The other contributing factor was the tire pressure was well below what is should have been.
I recently purchased the rims with the tires on them and I didn't bother to check the pressure. WRONG! Having 20psi of pressure in high performance tires, will make a knobby or humming noise too.

It's nice to be quiet once again.