97 Lumina 3.1L clicking, shaking.

Well I bought a 97 chevy lumina in november of '06 and all its been is a big problem. Ive replaced items such as the power steering rack, rotars, the alternator, etc. When I think everything is all great, my car is now shaking (not terrible, maybe normal?)At 50 mph and stops around 60-65. It also makes a clicking noise when accelerating, clicking faster as I move fast (sound like its coming from the passenger side wheel). The one weird thing is it doesnt do it all the time, sometimes you cant even hear it. Any ideas?