Strange almost scratchy noise.

My 99 TRD is making a strange scratching / rattling noise and it seems to be coming from the rear end. almost like a bearing is shot, but it is very spotty, i only hear it occasionally. any ideas on what it may be? i have a stock e locker but i do not think that is the problem.

 

have you checked the u-joints? same area and strange sounds can fool you.

I once had a rock "sliding" behind a hub cap instead of banging around as you would expect it to and that made me think I had something serious going on