96 C280 Shudder

[countman]

I noticed a shudder in my 96 C280 today. It only happens at speeds above 65 MPH, and then it is somewhat cyclical, occuring every 2 -3 seconds when at this speed. There is no vibration or shudder below 65 MPH. Possible tire balance issue? Flex Disc? I'm usually pretty good figuring out engine issues, but suspension problems really aren't my thing.

Thanks for looking, any help would be appreciated.