Humming noise only when towing under load
Hearing humming sound, could it be a bad wheel bearings, but only with a load, towing my boat. Or could this be something else?
Traveling with my boat trailer this weekend. I started to hear half way of my trip humming sound coming from the rear I assumed its the boat trailer for the first time. So I decided to sit in my boat while my wife drove my SUV for few miles in the back streets and heard no noise coming from the trailer wheels/tires. But when we are in the SUV there is an obvious sound or humming going on from rear of the truck but again only when I'm towing my boat trailer. I wondering if the bearings in the rear of my truck is failing slowly and only time I can hear humming sound is when there is a load in the back. Bearings on the boat trailer were greased and checked out few months ago so I don't think its the boat trailer but its possible too.
2013 Jeep Grand Cherokee unlimited with just over 36K miles. Towing Load is 4k tongue weight is probably around 600lb.
Thanks for any feedback or suggestion.