+1, first time I started my car after the uprated engine mount from BOE got installed, I thought my car would fall into thousand pieces lol. (OK, this is exaggerated).When I first installed my stiffer mounts, there was a resonance frequency of the tub I think that hit right about at idle and was REALLY annoying. But after about two track weekends, it settled down. I no longer joke that my driver's seat is also a back massager.
After a week, this will settle down. You can still notice a bit more vibration than stock, but not annoying at all!