we had the exact same scenario with our rally car one time. we were getting this bad drivetrain-related noise....whumpwhumpwhump when braking or coasting, went away under power. oh it's a driveshaft center bearing, it's a busted halfshaft, oh it's the clutch, no the trans, well mebbe there are SPOOKS down there someplace...
got into service, and one of the guys started to remove the left rear wheel. soon as he touched it with the lug wrench, he threw up his hands, "jayzus!! somebody tell me they already started to take this wheel off!" all 5 lugs loose, that wheel was just about to pass us on stage.
the lug holes in the rim were all ovaled out and ruined. so make sure to check yours, sounds like you ran quite a while with a loose wheel.
lucky you, it'd a sucked Big Time to have a wheel fly off on a 2-lane and make the car steer into oncoming traffic!