i can feel it mostly below 30mph. Also, i just got eibach pro kit intsalled about 2 weeks ago. I had it aligned after that. Almost feels like a break hangin up maybe? also over big bumps it really hits hard. almost sounds like something is loose.
Out of round tire most likely. The steel cords break apart and it makes the tread uneven. My Protege had a bad tire, and it would "thump" untill 20-30, then it made a humming noise after the thump went away.
^^^[rofl] could also have an egg in your tire...though bumps wouldnt affect that..and make sure if you loosened your shock in the rear for the spring install, that you tightened it back up...and make sure your lugs are tight ...good luck