wierd resonance, anybody else have this? Options

[blabla914]

OK. I'm going to try to make a long story short.

Last winter I did a six conversion to a 2.0L six with a rich johnson front mount with the club sport mounts. I am also using club sport mounts at the back. I originally fitted the car with a sport muffler. I finally replaced the sport muffler with a Bursch a few weeks ago. While the sport muffler sounded great I tired of my ears ringing for about 20 minutes after getting to/from work. I'm surprised my neighbors weren't throwing rocks at me, especially on those early sunday mornings on my way to an autocross.

Now that I've got a muffler that actually muffles I've noticed the car has a bit of a resonance at precisely 1900 and 2300 rpm. You kind of hear a waaaaaaaaaaa type noise and you can feel a little vibration.

Is this just the hard mounts transmitting some vibration to the car and resonating at these specific rpms or do you think I really have a problem?

Thanks for your help.

Kelly