LS3 Vibration
 

Guys, has anyone noticed that the LS3 seems to have a nasty vibration at about 3K RPM? I really didn't notice it until I tried some stiff motor mounts, but it was so bad I had to remove them.

I'm wondering if I need to get a new/better harmonic balancer or have my flywheel/clutch assembly checked. I have the ACT twin disk clutch, but I imagine that if it were out of balance the vibration would get worse as the RPM's increase.

Thoughts?