If that vibrating isn't your wheel bearing i'd try the Tie rod ends!!!!
About a year ago my car had the same problem, only mine happened at about 40-45. It'd start feeling pretty bad but i'd turn left or right even a little and it'd stop! I took it to merchants trying to get it aligned for general purposes and they said tie rod ends were MESSED UP ... tried to charge me 300 some bucks for it i said go to hell and give me my car
Anyway my passenger'* side outer tie rod end was completely blown. While removing it, the ball joing portion of the tie rod end seperated from the rest of it. The replacement was easy so maybe you should try it.. or try going to merchants and asking for an alignment and they'll tell you they can't do it, recommend their fixing it and you can say no and do it yourself. And you won't owe them anything!