When I press the gas every once in a while I hear/ feel a scraping sound almost like a loose washer or something and usually in low gears but sometimes in higher ones.
The exhaust manifold to down pipe connection on mine was loose because the bolts had rusted. Nothing else there had rusted, but the bolts were almost gone. super weird.
Poke around the exhaust manifold, my limited guess is a heat shield. Good luck.