Rattling sound from right rear
 

Rattling sound from right rear and bad smell? 2006 xk8

Could be a failed catalytic converter....

Could also be a failed right rear shock. The internal valve snaps off inside the shock and rattles around driving everyone in the cabin nuts unless the ragtop is down. That would not account for the bad smell, however....

Failed upper shock mount? Outside chance the smell could be due to the foam falling on the silencer ?

Maybe a heat shield is loose.