drivetrain "harmonics"
 

My truck will make a low grade harmonic humming from between 30 mph to around 50ish, depending on load.
Seems to be coming from the passenger side of the hump in line with the seat front.

Is this normal?

Jimmy

Just a guess, if your exhaust is stock, there is a metal rod/support brace that is welded on to your exhaust pipe, and fits into a grommet on the trans support bracket. There is a rubber grommet that the rod fits into. If the grommet has failed or is gone, that might be the cause of your niose.

You need to crawl under the truck and check (follow the exhaust pipe). It could also be a lose trans mount, but, just guessing.