Hey guys. I have a 2000 DRZ400S. I bought the bike needing work. It had compression problems. I disassembled the top end and found a blown head gasket and bad rings. I replaced the piston, rings, wristpin, top end gaskets, and the spark plug. I also had the exhaust valves replaced. The bike runs great and I'm having a lot of fun with it. My concern is.there's a vibration coming from the engine that seems to be happening mid throttle. It's not present at low rpms and I'm pretty sure its not present at high rpms. Speed doesnt seem to be a factor but engine load does seem to be a factor. I can feel the vibration mostly through the seat and the engine has an echo type sound and seems to bog down a little when this occurs. Any ideas on what is causing this?