Noisy front wheel bearings are common. They sound like an airplane engine, and the sound can travel making it elusive to find. Also look for a broken or deteriorated rubber exhaust hanger that is letting a pipe rub against the body.
There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.
SPONSORED LINKS
Thursday, October 4th, 2012 AT 10:26 AM