I have a 52 KV6 3 door. Been trying to trace a rear end clunk since last year when the rear shocks were replaced. The car has plenty of other little issues, and it is possible that the noise was developing before the shock change. Its the wife's daily driver (and she is oblivious to the noise even now), so I can only say I noticed it after the rear shocks were replaced.

The noise seems to come from mid to rear OS and is related to rough surfaces, and can be heard clearly (but fairly quiet) at low speeds, straight line or cornering, making me think it is suspension movement related.

Having been underneath it several times, I have replaced the trailing links on both sides (bushes had loosened up but no sign of metal hitting metal), checked the link rod bushes for movement (all good), replaced the diff mounts (front one gone but a different noise and related to drive being transmitted), checked the subframe mounts (all strong and located properly), and checked everything for movement. If I bounce the rear of the car while stationary I can here the shock plunger moving up and down (same on both sides), and walking alongside the car while the wife is driving it on a rough surface, with my hand on the rear wing nearest the top of the strut, I can feel a vibration when a bump is hit. This makes me think strut top mount or top bolts not tight.

Any one with similar experiences or ideas out there?

Next steps for me, maybe next weekend, is to take out the rear OS boot trim and check the mounting bolts and the nut at the top of the strut for tightness. If that is all good, I will drop the strut off altogether to see if everything is seated OK.

Ah well, I guess I have hit upon a brand new Hippo noise.

As I investigate I will update in case anyone else comes across it.

The only thing that comes to mind is the exhaust back box can move around quite alot and make a big clunk. Try a couple of new rubber hangers before you do anything drastic.
Mike

Have you checked the drive shafts for movement? Had a similar clunk from mine but at the front.

Mine had a clunk due to the 4 bolts holding the rear sub frame up were slightly loose, the sub frame "knocked" when turning or bumps

Thanks for the ideas. I know the subframe is tight as I checked for the captive nut issue that seems quite common on earlier ones. The exhaust is a good point. The rubbers are intact, but the OS one is certainly past its best and looks quite stretched. I will check the drive shafts as well, as the diff mounts were quite shot, and the movement might have worn the inner joints.

Top strut mount all seems secure. There are 2 relays in that location that are meant to be mounted onto tabs on the bodywork but were hanging loose. Doubt it was them, but they are secured now.

On to the exhaust and drive shafts next weekend.