Well I have yet to investgate this, but around 4500-5000RPM there is a pretty heavy vibration.

It goes away after 5200 or so, but mostly occurs when in the powerband.

Doesn't occur all the time either, normally for about 20 minutes after a cold start. After running at normal operating temp for a bit it gets very faint when it does occur.

I believe it is something vibrating against the firewall as I can feel it, along with hearing it. But it may just be the heat sheld on the cat. Like I said I have yet to investigate.

The main reason for this post is to get some ideas as to what it might be. Maybe someone has had this problem as well and can give me a little insight as to where to start. Definitly think its on the passenger side.

Motor is equipped with I/H/E, airram, lightened crank,W/P,PS pullies. If it matters.

 

well, i do know how to help with the good vibrations...

http://www.youtube.com/watch?v=zJgXxQpsUhY...t=1&index=4

 

never had this happen to me but i suspect it's your belts. i don't know what else it could be. ever tried revving it standing and seeing if it still happens? i can't help much with this. you seem like you know what you're doing.