ok so here's the deal...in the past few months I've gone through and rebuilt my rear end with new 4.11gears and auburn carrier. Had my driveline balanced and HD U-Joints put on. And finally, put in a newly rebuilt 4L60E from MegaMaxTrannys down in Floriada. I also put on all new suspension (eibach Sportlines, Kyb AGX shocks).

Well i just got the car all put back together, and it has this nasty vibration/rotational sorta metal against metal sounding clunk, but only at High speed 70+. It also almost totally goes away when i'm on throttle. I just went through the bottom of the car earlier today and put on a new tranny mount hoping it was just some slack in the old one. Didn't change a thing. It sounds like its coming from the area of the front U-Joint...right where it meets the tranny. So i crawled under and started pushing and pryin' on things trying to find slack...the only slack i can find is right where the driveling connects to the tailshaft of the tranny, if i push up the tailshaft and driveline together move up a tiny bit, is this normal? I assumed it was since my old transmission (sitting in my garage) has the same amount of slack in the tailshaft, and the one i just put in is brand freakin' new and had slack some slack in the tailshaft the day i pulled it out of the crate. The only thing that concerns me about the tailshaft, is i had to reuse my old tailshaft housing on the new tranny, so maybe the clearances in the housing are way off. The other thing was during reassembly my driveline ate **** falling off a table. It was standing on end, and fell the length of the driveline landing on the front U-joint, couldn't neccessarily feel any slack anywhere, and drivelines are pretty tough, but anyone think that fall would be enough to screw it up?

Anyways, it also makes 1 clunk if you are coasting and hit the brakes suddenly. But, i can launch hard and go WOT to the top of 4th, and there are no bad sounds. But soon as you're on the freeway cruising 70 or 80ish at light or no throttle you hear this rotational clanging, sounds like metal vs metal...after searching the board the one thing i hadn't thought of was exhaust hitting hte driveline, so later i'm gonna put her back up on jack stands and see if i can find marks on the exhaust pipe showing contact.

Sorry for the huge post, but after putting all this work into the car, the last thing i wanted to hear was clunk noises. Any help/ideas will be much appreciated.