1998 Oldsmobile Aurora highway shimmy

I've been experiencing a slight wheel vibration when driving on the highway. The vibration starts at around 60-65mph and it doesn't go away. I have had the suspension checked several times by 9 different mechanics. Had both wheel bearings replaced. Brake pads and rotors have been replaced. Shocks/struts have been replaced. New Michelin tires have been road force balanced with great numbers. The tire shop found a rim that was out of round and it was replaced with a good used one. After all these repairs I still have a shimmy. It seems that it varies in frequency and it doesn't vibrate in all roads. The last thing I was told is that the CV joints might be going bad, but I really don't understand why because they are not making noise.

Any suggestions?
Thanks in advance,
G