First, check your oil, make sure there is enough oil. If there is, it's probably either the gauge messing up, or you have bad oil pressure and you need to have it checked out. As for the rear end, crawl under the back of the car and in the middle of the rear axle is this round case looking thing, that is your differential. There is a plug in it that you will need a medium socket wrench (with no socket attached, just the square end of the wrench) to unbolt. Then get a thin "L" shaped piece of wire and stick it in the hole where the plug was with the short end of the wire pointing down inside the differential. If the wire has oil all the way up the short end up to the bend, then youre ok on diff. lubricant, if not, you may have a leak. If its not the diff. making the noise it could be the tranni. The tranni mount could be loose.
EDIT: I didn't read your post well enough the first time, but its probably NOT the diff. but it wouldnt hurt to check the diff. oil. Because if you have a leak and didnt know it, by the time you realized it it would be too late and your diff. would be shot. I think your clicking noise is the tranni. Bolts in the tranni mounts may need to be tightened or replaced. I used to have an 89 camaro that that happened to.
