Could be an out of round tire. Have the dealer road force it. Balancing it won't solve the problem. If it fails road force, it might be able to be force matched by dismounting and remounting the tire to cancel out the high spots of the whole assembly. If it can't be force matched, you need to replace the tire.
I've been noticing more vibration but I know it's the motor because if I step on the clutch it goes away so it can't be tires or driveline. We don't drive kilometers here so it happens between 75-80 mph which is our normal freeway cruising speed. I feel it right up through the floor board and the shifter. Any ideas?
2008 Audio A4 Cabriolet Quattro
Possible CV joints. When you step on the clutch the CV joints "unload" and can be fine because the ***** are being driven from the wheel end of the drive line. I have had dicey clutches that had bad springs between the friction surface and the splines that caused vibration when loaded, but nothing when the clutch was released.