94 Cougar humming

My 94 Cougar 4.6 is humming at any engine RPM. It will start either by starting the car or by tapping accelerator or just by driving it. I duplicated the problem and the humming comes from where the tube that goes into the DS valve cover into the air runner and the mounting bolt for the runner. I took everything apart and cannot find anything wrong. Put new airfilter and cleaned out the throttle body and remounted the rubber seal on the runner. Anyone know anything? Drivin me nutty.