91 16V - Whenever I go over a bump in the road I get a rattle that sounds like the boot lock being loose. However, It seems fine to me, locks and opens fine and the boot doesn't budge when I try to lift it up and down when locked.

There's nothing loose in the boot; so if it is a faulty lock mechanism, can I just change over the locking mechanism or do I have to change the key barrel as well?
Ta.