guys how do u know if my USM is faulty? how do i check?
If you have a friend with the same body / lens combination, check to see if the other camera also behaves the same. If it is, then nothing to worry about. If not, swap his lens with yours. If your camera body and friend's lens is okay, then your lens is the problem. If your friend's camera and your lens is okay, then maybe there is something wrong with your camera body.