I'll start with the exhaust setup.

LS1 JTR LT's w/1/2" three bolt flanges 3" collector
Stainless Y-pipe with flex joints on each side 3" pipe to 3.5" out
RB catback

What I am getting is a VERY metallic rattle on accel and decel. It is MUCH more pronounced on decel. The motor does not have to have any load on it. Can be done from blipping throttle under the hood. The noise started after I removed the old 2.5" catted y-pipe and replaced it with the SS 3" catless pipe. I cannot see anywhere that the pipes are rubbing(verified lack-o-engine movement) and I have even used the graphite crush gaskets to ensure there isn't an exhaust leak. It's mostly coming from the passenger foot well area. I've had the LT's off a couple times and not been able to find anything. The JTR LT's have a little play in how high the flange can be tilted(pivot at heads). My flex joints allow me to mount them up or down. IE more or less ground clearance. It doesn't change anything. I'm really at a loss.

Any ideas?

 

put a rotary back in it... the rattle should go away!!! lol
sorry i couldnt resist!!!

 

If only the two had anything to do with each other. :-(

I actually like the sound and power delivery of the rotary. However, everything else leaves a bit to be desired. I get way better mileage. The power is great for the mileage. After running 420+whp for over four years and my only issue is a metal clank from the exhaust I put in it, then I'm okay with that. I just want it to go away. Hence the post.

 

Given that it only occured after you changed the Y pipe I'd double and triple check any of the flange bolts. Obviously it's hard to know how pronounced the rattle is sitting here at a computer desk. But even the tiniest of exhaust leaks can cause any order of odd noises.

 

It's VERY pronounced. It's very obvious to people outside the car. No where near deafening. But certainly noticeable.

I'll give everything a once over again.