[shorod]

Welcome to the forum!

I think you're missing something or not accurately stating something. Just about all of the items you have looked at would cause a noise to change with vehicle speed. The faster you go, the higher the frequency of the thumping. But you state that the thumping does not change with vehicle speed. That would say that it cannot be associated with the drivetrain.

Is the thumping present when the vehicle is stopped? What if you put the vehicle in neutral while firmly holding the brakes and slowly increase the engine speed? Might you be experiencing a misfire? Also, make sure you don't have a chunk of ice or something that's stuck in an area and it's bouncing around as you're driving. Since you're in MN, did this just start happening after a recent snow by chance?

-Rod