You don't mention when you hear this noise. Is it anytime the motor is running? Under acceleration?, Braking?

It could be a broken weld, broken motor mount or anything that is causing a metal on metal "squeak". Check your exhaust hangers, spring hangers. I had a broken weld on a rear spring hanger that took me a while to figure out. Just caused an annoying squeak. Until I saw the rust, I couldn't find it.