Noises under the car

My '97 has high pitched noises at 1000rpm, in gear, with or without the car moving after the motor warms up. The noise seems to come from the area under the back seats underneath the car.
thanks in advance

not much under there except drive shaft and muffler, check for exhaust leaks. also check for loose or broken hangers or missing rubber mounts.

my exhaust sqeaks a little because they put in an oversized catalytic converter and the bracket barely fits with out the rubber.

Thanks Eric,
The muffler has a slight rattle when I hit it with my hand...I just haven't hit it hot.

do you have load leveler shocks? if so it could be compressor whine occuring at low RPM due to low amperage being generated, a condition that would clear up as the enginge revs up.

Nope, my load leveler is not electrical, she sits on the passenger side.....lol