I have a '97 Civic coupe with B20B swap and turbo, and I have been getting a really bad vibration at 3000 rpm, at any other rpm it feels fine. Wasn't sure what it could be considering it was only at that specific rpm. It started a little while after I put a new turbo kit on, and the downpipe needed a little modification because it wasn't long enough to reach the cat (ebay kit). I took it to an exhaust place and they welded a pipe on the downpipe, and then to the rest of the exhaust piping. After I got that done, that's pretty much when it started, at first it wasn't too bad, but it seems like it got worse. I looked at the pipe they welded onto the downpipe and it actually looked like a smaller diameter, I was thinking maybe there's some type of harmonic issue because of that or something....I figured it would probably have to do with the exhaust somehow, because the vibration started after I got that pipe welded. Any other ideas? I also have Avid mounts, so there's a lot of vibration anyway, but there is a very pronounced vibration at that specific rpm. Some other info on my car: the rest of the exhaust is pretty much stock, I think when I bought the car, it had just a Greddy evo axle-back exhaust kit, the turbo is a xs power t3/t4 turbo kit, pushing 9psi, all stock b20b motor, ls tranny, exedy street clutch, tuned with Hondata s100.