Noise in rear passenger area?

[Jimls]

I had the same rattling noise when going on rough roads etc. drove me nuts. Corrected this by inserting a 3" x 1/2" piece of black weatherstripping foam between the rear window and the panel that holds the subwoofer. There is a small gap between these 2. I squeezed this in pretty well dead center of this area, it is a tight fit to gets your hands there due to the angle of the rear glass and also made sure that it was not visible from the exterior view. Excellent result no more noise and back to sounding like a vault inside. Also check the interior panels on the rear pillars as these may rattle also when going over bumps if not secured properly from the factory.

[timandmax]

If you have not heard from others yet, the rattle/clunk when driving over rough roads, manholes, etc is the result of a defective right rear shock absorber KNUCKLE. I, and dozens of other 08 CTS owners have had it corrected by dealers, who by the way were issued TSB's as far back at Jan of 08 on this problem. Some dealers are replacing BOTH the knuckle and the shocks, some are only fixing the involved RR knuckle. It WILL correct the problem. If you go back far enough in the Forum posts, you will read many discussions and even details of the TSB and what to do about it.

[newcadillacguy]

I have had the same experience on my '08 CTS4 DI... the passenger side rear area sounding like a "clunk" when traveling over bumps, etc... After reading a different thread on the forum, the suggestion of the "F Knuckle" replacement was identified. I printed out the specific items from the thread and brought it to the service department of my dealership... While this new to them, they supported my concern and ordered the part... They fixed it last week and the "clunk" issue has been resolved... I have traveled on the same roads where I know I can hear the sound and, fortunately, I have not heard anything... While its only been a week, I believe this was the rememdy...