I dunno but F.I. exhaust with 12" res is pretty quiet to me until around 3k RPM... I'm not sure where people are getting that the F.I. is even that loud. Maybe with no resonators or on cold start but I'm sure HKS would be similar.

Even with the 18" res option, my FI's annoyingly loud on cold start, but that initial burst goes away after 30 seconds or so, and the volume keeps ramping down as the car warms up. Driving or idling, I'd say it's pretty tame when you're not on the gas hard.

Loud/quiet is just an opinion. However, I know thru experience that the HKS is a lot quieter than the FI 18" CF exhaust..... A LOT quieter. But both sound like pure sex.