I feel very confident you rasp is from this, as mine was. I would research a y pipe that has a HR design merger and the appropriate inlet and outlet you your art pipes and rear muffler section

 

Theres no point of him gettin a y-pipe unless his plannin on selling his HKS.

Buddy of mine had crawford hfc & hks exhaust and had rasp like a honda.
Switched to a X-pipe instead of his H-pipe solved his problem.

Im not sure if u read the post someone posted on here showing the low quality welds the inside of the H-pipe from the HKS exhaust has. Might be the problem.

Good Luck!

 

That does make sense, but what about the Stillen exhaust? Im running that now with the test pipes, and thats what the video above was of.

 

If your exhaust combo is a combination of different inlets & outlets. That plays a big factor on the flow of the heat inside the exhaust. causing hissing & rattles.

If you run an oem HR/DE y-pipe with HFC or TPs your always going to get some sorth of noise. Since hfc/tps outlets are 2.5"-3" & the y-pipe inlet is 2"-2.25"

I might not be right but thats what I learned from my experiences.

 

Im definitely going to take this info down and see what i can find out to be best. Thank you very much for your help. In the mean time, if anyone else has any ideas