2001 Chevy Cavalier Strange noise on my poor Chevy

I've been driving on a couple of forest roads in West Virginia and since then, a strange noise is occuring each time I go on after braking.

To depict it more clearly: I'm driving, I brake and come to a stop and when I go on again, a thump or light knock occurs (coming from the back).

At first I thought it was something banging in the trunk, or the exhaust pipe. None of these. A mechanic saw it and told me it was the struts (which could make sense since the forest road driving) but if the struts are in front, why does the noise come from the back? Sounds fishy, besides, the mechanic is charging an awful lot (more than the price of the car.). He's telling me that it's not so important anyway and that I don't really need to do it, there's no safety issue (it doesn't sound quite right).

Do you really think it sounds right? (Without seeing the vehicle.) Or what else could it be?

Thanks for the help.