Baloo588

Its a very small fine vibration and feels like you are going over a coarse road surface when you are really going over a smooth tarmac. I am curious if this is a simple balancing of the tire/wheel in the rear since it comes at around 40 mph and goes away at around 48-50mph? Its a strange vibration that I cannot pinpoint it when I am sitting in the back seat and someone else is driving the A8L. I put it in neutral when it is coasting and still feel it, so it cannot be transmission related. How about wheel bearings??? BTW, the tires are pirelli p6s, and I have 2 new ones on the back wheels and 2 old ones on the front. They will be replaced in 1-2 weeks with Yokohama Advan S4. But I just want to be sure that it is a simple balancing problem with my current tire/rim that is causing this vibration and not the wheel bearings, etc. My car has 112k miles on it.

MP4.2+6.0

Start w/ the simple--tires. Charitably, those Pirelli's are not known as one of the better tires out there, especially as they age and wear--noisy and rough feeling.

Then of course the basic tire balance. You will have answers on both as soon as you get your new tires.

After that, yes wheel bearings as you say. Low rumble, maybe a bit of vibration. Noise tends to worsen a bit when turning opposite the side where the problem is--that is, when the load shifts more heavily onto that side with the bad one. Tends to be in front given the loadings, but could be in rear on occasion.