Originally Posted by ped

The Fast Intentions catback with stock cats were ricer loud with massive 100db+ (measured) drone inside the car. That will literally make you deaf over time. The drone was headache-inducing.

The HKS, in contrast, uses Helmholtz resonators to remove all sound at the frequency that resonates in the 370Z cabin, for a drone-free experience. When you're idling along it sounds little louder than stock, but put your foot halfway or more into it and it wakes up with an aggressive growl that still is never annoyingly loud. It's what a sports car should sound like, IMO. It's more expensive but oh so worth it.