Just noticed a thumping coming from the left rear wheel area. I recently had a 1300 pound granite block in the bed and did at the same time tow a 4000 pound boat. The tongue of the boat trailer is messed up so it rides very low and puts a lot of weight on the hitch. Could that have anything to do with the noise?

 

Need a little more description of the "thumping". Sometimes, my truck will thump "one time" when I accelerate from a stand still. It feels like someone hit the frame with a big hammer. But it's the tranny bands 'grabbing'. Needs a fluid/filter change.
If yours is continuous and the same frequency as wheel rotation you could have damaged the left rear wheel bearing race. It's easy to forget that 1/2 ton is only 1,000 lbs carrying capacity.


Confucius say "Always put 1300 lb granite block in the 4000 lb boat"