I have a 2003 xk8 with about 80,000 miles on it. there is a vary loud clunking sound coming from under the hood when I go the slightest bump in the road.

 

I had a similar situation (low speed bumps), turned out that the anti sway bar hold down bracket lost its bolt.

When this occurred I could move the sway bar around by hand grasping it at the end behind drivers side wheel. That's just an FYI.

The missing bolt is obvious if you look.
Put hood in service position.
Goto front corners, by where you'd access high beam bulb or forward facing driving lights.
Look down, see sway bar, there are bolt/brackets at left and right outer area (not talking about the big brackets in front of radiator.

I hope this is the issue, real easy to fix. Bolt commonly available in auto parts store. You'll need a long (like 2 feet) wratchet extension though.

If this is issue, I believe I posted bolt size and more detail instructions a couple of years ago.

John

 

What John said, but check the shock mounts at the top, they do make the clicking noise also when worn out.

 

Ditto on the front upper shock mounts. It's usually easy to tell if they have failed because the shock shaft top nut is no longer centered in the mount, and often the foam rubber bushing is turning to powder.

Cheers,

Don