If its just a quick squeak as the suspension moves it could be shock or spring bushings squeaking a bit. Try shooting them with wd40 real quick and see if it goes away. Doesnt cost but a couple $$$ for a can (should have one around anyway) and if it doesnt help it wont hurt.
90 YJ 5.2 Magnum, AX-15, 231 SYE'd
D44 front, welded/trussed AMC20HD rear. 4.56 gears soonish.
Western 6 lug aluminum wheels, with 35x12.50x15 Wrangler MTRs