fbodyfreek

my car likes to rattle really hard between 4000 and 5500rpms under WOT and it rattles pretty much anywhere when cruising at speeds of about 90mph plus. i do have a polyurethane transmission mount, but the problem was there before i replaced it. and i now have an aluminum driveshaft and it still rattles hard when approaching speeds of 100mph. also i can feel a slight bucking at idling, but i don't have a cam and the rpms don't flutter. it's just like a steady pulsing. i was under the car yesterday while installing my transmission cooler and noticed the the harmonic balancer wasn't rotating in a perfect circle. it didn't seem right and sorry if it's a stupid question, but is this the culprit of the problem? if not, are there any ideas? thanks.