'98 Sebring has a rattle in the back

Hi there.

My husband drives a '98 Sebring that has a rattle coming from the trunk area. It really sounds like its coming from both wheel wells. It sounds sort of like there is a loose propane tank rattling in the trunk. My husband says I shouldn’t worry and that I’m paranoid. However, the passenger-side front wheel fell off while he was driving one day, so I think I have grounds for worry and paranoia!

So, what do you think it is and should I have it fixed??