Ive had this knocking for a 2/3 years now its not really got much worse, but I think it's nearly time to get it sorted.

It comes from the rear and its only quite faint, it can only be heard between 10-35mph and then it seems to disappear somewhere maybe its just additional car noise drowning it out.
It also only knocks over very small bumps/ripples in the road at these speeds. If you go over a large bump or pothole you cant hear it.

My Jagman says its some bush at the bottom of the shockabsorber which he allows 2 hours per side to do and normally means a 200/50 pound bill.

I dont fancy this on something you can only hear 25% on the time.

 

You didn't forget to let your mother in law ou of the drunk, did you?

The mechanics suggestion sounds to me like a fairly likely soluion. The metal parts have rubber isolators. If the isolators get worm, then some movement can rattle. Large movements "bottom out" the isolators and no sound is heard.

 

Shock bushings are gone. Doing mine too.

 

Or maybe the rear stabilizer links ?

2 Rear Stabilizer Link Set for Jaguar XJ8 98 03 | eBay