Therein is the advantage(s) of spinning the tire while it is mounted on the vehicle - not on the tire-balance machine. Loose bearings, bent rims (often caused from wrong-sequence tightening), sloppy tie-rod ends, are easily observed under (almost) road conditions. Another possibility places vibration within the driveline. An out-of-balance driveshaft, or clutch assembly will also set up a 'thrumming' at harmonic speed which is transmitted through the frame to steering wheel. Heck, I once experienced a bent generator pulley that set up a terrific 'flutter' sound - but only at 40mph or so. Drove me nuts. Until the fan belt polished the tight spot. Just before it shredded. That's another cap Big Bolters wear - a hunting cap. Tracking down the elusive 'Gremlins'.
