When i plug in my trailers i get a buzzing when pushing on the brakes if i unplug the brake controller at fuse block and push brakes no noise at all the buzzing only happens when brakes are applied with trailer connected that has electric brakes i went to hitch guy and we tried new box and no luck i have aftermarket stereo and amp i tried to look over everything but no luck please help before i go nuts thanks alto

Ground loop. Could be tough to find, but trace where all you connections for the trailer box and the stereo run and connect. Check to be sure you don't have any broken factory ground straps.
John