I doubt the 65mph vibration is due to the tensioner rattle. If it was, you'd get the same vibration any time you were operating at the same RPM. Since the vibration is vehicle speed dependent and not engine RPM dependent, it's in suspension or driveline.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]