I have had a vibration that was noticable at 65 mph plus. I had the control arm bushings replaced solved a little bit of the vibration but not all.

I asked around local shops and found out that many cadillacs had a problem with the tires being out of round. Was told that the Hunter GSP9700 was the answer. It is about a $35,000 balanceing machine. http://www.gsp9700.com/

Had it done today and all vibrations are gone. Cost was $8.50 a wheel plus tax. Well worth it. Usually only found at good tire shops and highend dealerships.

Everone who has this vibration should check it out and even it you dont have it done anyway it will improve gas millage and millage of your tires.

Makes me love driving this car at highspeed just like it was designed for. If only we had The Autobahn in the states I wouldn't mind cursing to work at 125 but hey that just me.