hey guys was just wondering if anyone else has ran into this situtation because i cant seem to find out what is causing this. I bought and installed the aps test pipes and greddy evo II cat back. i've checked and double checked torque specs on all bolts and absolutly everything underthere, but when the rpms are dropping between 3000-2000 it makes a hissing/high pitched rattling noise comming from near the motor somewhere. this is the only time it does this, not when rpms are climbing, or when rpms are falling durring any other range. thought it was a leak at first but dont have any....anyone else have this problem or suggestions.

thanks