I just got done installing my start today, and now with the car sitting at an idle in drive, the car has a noticeable vibration that wasn't there before installation of the starter.
NOTE : I did have to drop the Y-Pipe down and reinstall it to get the starter out and back in. I am also hearing a knocking sound every once in a while. Is there a possibility the exhaust is rattling against something under the car and causing the vibration as well?

 

Quite possibly... Dumb question, but are teh fittings on the y-pipe tight? My brother replaced his starter and that was what was causing the rattling

 

i'd look to the exhuast before anything else. I had this exact same problem not long ago and it turned out to be my drivers side header flange touching the frame and vibrating like crazy. Just loosen everything up a little bit and adjust it so it's not touching anything...

Eric

 

I am going to climb back under there sometime tomorrow and take a look. I hope that is what it is. The y-pipe is nice and tight up against the headers. I just don't see how that could cause such a vibration, but I assume it is possible. It only really vibrates when the car is in drive at idle, and goes away when accelerating, but then starts the clicking type noise periodically.