I've got a clunk in the left rear that makes the noise only when going diagonal over a speed bump or driveway curb. e.g., same axle: first one wheel, then the second. There is no noticeable effect on driving, nor is there any noises when both rear wheels jounce and rebound at the same time.

I've checked and double checked:
New sway bar links and bushings and bracket mounting bolts
New lower shock bushings
Tightened upper shock plate mounting bolts
Tightened all major 19 mm and 22 mm bolts holding subframe to body, etc., incl. lower rear swing arm.
Used a pry bar on all the major bushings and found nothing loose
Cleaned out the trunk and removed everything incl spare tire and jack package.
Checked exhaust system fasteners, rubber and associated clearances

I recall someone posting about a loose part in the convertible top boot, like near the lift cylinders and I am thinking that maybe the noise is coming from there. It almost seems like the noise occurs when the car is being rocked side to side. or twisted under compression load. Any ideas?

 

Loose nut behind the wheel.......

J/k (couldn't help myself)

 

GordoCatCar,
you may try looking at the transmission mount. The mount is a metal plate with a lot of hard rubber, creating almost a cradle, the rubber had completely cracked and was broken. The problem was that you could not see the crack until the mount was removed because the weight kept the rubber pieces looking as if they were still one piece, but it was not, so presumably when the cover goes over a bump it easily separates and then comes back together creating a clunk or thud that could be heard. Just a thought because this is exactly what happened to me. A new Transmission mount solved that problem!
Good luck and

 

Gordo,

FWIW I had a similar problem with my 07 XK. I turned out to be a leaky right front shock that I had been ignoring for a few months. So, just for grins, check for leaks on all of your shocks.

Sound can originate from strange places and transmit in strange directions on these uni body cars.