im running stock ls headers down to 2.25 piping back to a 00si muffler no more heat shields and the problem isnt clearence or the muffler or holes i beleive...i was just wondering if haveing no cat might be the cause of this rattle from aprox 3-5 rpm its the worst
and feedback or ideas would be appreciated
thankyou

 

is it while you are slowing down?
if it is there is a peice of metal on inside the b pipe (bottom piece of the header)
that breaks its a very common problem on 94-01 GS-R's there is a service bulletin
on it

 

Did you put the springs on to the bolts, back on where the header and cat pipe meet?