My 03 C240 starts to shake wheneverI go over 70mph. What could be causing this?? Also, whenever I got over a bump, it squeaks like an old mattress...what do I need to replace and how much will it cost?? Thanks for any help

 

I have the exact same problem. My car shakes a lot between 60 - 70 mph and after 70 it vibrates a bit.
When it goes over minor dips, especially on right turns, I hear a squeaking sound.

Tyre balancing should sort out the shaking problem, IMO, and the squeaking sounds are due to broken sway bars at front or something like that. I am taking it to a mechanic this weekend to fix that.