I own a 2007' Mazda 3S (2.3) Whenever I get up to about 45mph and above my car vibrates/shakes. I used to be able to really feel it in my steering wheel but that's gone now. I took it to a mechanic who balanced my tires, (said my alignment was fine) and yet it still does this. What else might the problem be? Cheap tires?? If so would you recommend any tires?