1997 XK8 Noise towards the rear
 

The noise is lower in pitch and not consistent. It almost sounds like an old clutch trying to grab hold. It's coming from the back seat area and low. The sound is not present when accelerating. It happens especially around a constant speed of 35 mph. So, during acceleration, nothing, then stabilize speed, it comes in and out. Any suggestions? Thank you in advance.

If its rotational and not bump related, wheel bearings are high on the list. Then Warped Rotors, sticky brake caliper, parking brake issue, then drive shaft joints. Half shaft joints are less likely to make noises, but it they are -yikes - get them replaced.

With the body on jackstands in back, you may be able to pinpoint the noise.

Thank you Ungn. What is involved in replacing wheel bearings? Is it a tough job?

I have not done the rears, only the fronts and its a bit of a chore.

The back maybe not so much, once the axle nut is off. The upright seems to come off/go on easy enough (if you remember to mark the eccentric bolt clocking) My back bearings seem still good so I haven't touched them.

In front, bad bearing growl and the growl would get louder when changing lanes. Don't know what would make the rears louder.