by "they" i assume you mean a shop. i would think they would check the u-joints first if you heard a noise when you went into reverse., but you just may wanna do that yourself, to be sure. feel free to post a thread in the lounge. then more can help you in one area.
(from another thread) I haven't checked the U-joints, but I have had it to two shops who both said it was the rear end.... I wish I knew a mechanic I could trust, and how can I check the U-joints to know for myself?