one bolt fell out and it sounds awful only in reverse

I have a 97 Buick Centry and a bolt fell out tonight. the car sounds awful in reverse, but fine in drive... any idea what bolt it is and what the problem may be?

Welcome to AF.

Hard to say we could only speculate as to what bolt you are referring to.
Can you describe the bolt or post a pic of it?

Could be anything.....engine mount or subframe bolts.