scraping noise?

on my 91, when I go over some bumps in the road, not all of them, I get a short scraping noise coming from the left rear I think. I have looked all over while on my back under the car and cannot see anywhere anything is rubbing. the tires are definitely not rubbing on the fender lips or anything. Anybody have something similar?

I did add ST 1.5" lowering springs, Koni shocks, 255/50 17 tires on 17 x 8 rims, new front upper and lower control arms and ball joints, new strut rod bushings, new trans, motor, and diferential mounts and bushings. I also swapped to a 94 gas tank and a 90 rear sway bar

Could it be the gas tank heat shields? I cannot see any scrape marks but you can move them around a little. If I can get it up on a lift I might be able to see areas not seen while on the ground but I still cannot figure out where to look

Any help will be most appreciated

Ron

glxieman@yahoo.com

Hello

Hello,
I know that you might not think it is your tires rubbing against the rear fender but I'd check that out for sure.
Your over all tire height(27") is a bit taller than stock(26.68"). You also have to consider the following, driver weight ,if you have a speaker box in the trunk. Does this happen all the time or when you have a full tank of gas. If you have the exhaust outlet in the stock location it may be that as well.
I have a 2"drop and 18" wheels. When I was running 255/45's(27" overall height) I had problems when I had a full tank of gas and a trunk full of junk he he.
Good luck man,
D Rainer