When I apply the brakes I here a mettalic POP/THUNK noise coming from under the front passengerside. It is inconsistent during normal driving but if I hold the pedal so that the truck will just shift slightly when going from reverse to drive or vise versa it will do it almost every time. BTW it is an auto. Any suggestions? I thought it might be the track bar unloading but I'm not so sure after sitting in my parking spot going from drive to reverse for 15 minutes today.