I recently got my parents 03 expedition and it has a thumping noise from the rear going about 20-30mph and i thought it was tires so i put new tires on it and didnt fix it... My boss who has been working on cars for 30 years and has an ase. And we put it on the lift and he thought it was the rotors because were warped. I turned then and it is still there. Btw we herd nothing that was put of the normal like bearings struts or anything. The car used to sit for months at a time.. Has anybody had this issue? Should i worry about it?