Ok,I have brought my car (2005 Toyota Echo) into the shop three times and they can't figure it out. I have summer and winter tires. Last summer the summer tires were fine, the winter tires were fine, then I changed the front tires, and couldn't remove the back tires (I hit them with a hammer and 2x4 and they didn't come off). From that point on my car has vibrated at around 60mph, but not 100% of the time. I took the car in to the mechanic, they changed the back tire for me and balanced the front...still vibrates, they then balanced the back...still vibrates. Now they say the disk rotor is bent, and want to fix that but aren't sure that will fix the problem. What's going on, I changed the front tires and now the car vibrates at high speed most of the time, but not all the time.