travel trailer brakes

had about 10 minutes of free time today...long enough to hook the cord to the truck and check a couple quick things...the brake lights do come on on both the truck and trailer when the truck brakes are applied. When the truck brakes are applied, I can't hear any hum near any of the 4 wheels, however when the slide lever is applied on the brake controller itself, i can hear the hum on 3 of the 4 tires, the two on the curb side and the rear of the other side, and nothing or very slight on the one on the front tire of the other side. The blades and the slots on the plug and the truck are all clean and clear...I also pulled the break away switch and didn't hear any pulsing at the tires. hoping to get a bit of time tomorrow or friday to start pulling tires and visually inspecting the brakes...on vacation so tinker time is hard to come by when it's meant to be family time. any other thoughts and leads would be appreciated...thank you to the two that have posted so far...helpful info so far. i like the idea of the rewired brakes