vibration at 2500RPM (M3S)
 

So I replaced the engine coolant this past weekend, and part of the purge procedure is to hold the engine RPM up for multiple minutes. I didn't quite do that, but in the process I noticed a vibration when holding the engine revs at 2400-2500RPM.
I've been chasing a similar vibration at 55-60MPH - and that's at the same RPM range, so maybe it's not my tires, but some engine issue.
Has anyone else run into the engine vibrating - yes it feels like a tire a bit off balance.
Note that i've stiffened my engine mounts with silicone, and will shortly be modifying that a bit. The reason is that the mounts are too soft for me to feel the clutch bite point, firmer mounts = better feel for the clutch.

Thanks