I have the J2 Exhaust catback and it's most definitely louder than stock. Probably louder than the HKS exhaust but not by very much. When revving there's definitely some burbles and occasional backfire pops but not too loud that it'll attract unwanted attention. With a SRI or CAI the burbles and pops are more pronounced and since I'm on the stock airbox the exhaust has a slightly quieter burble and pop. Sounds great and has a very deep throaty sound which I personally like compared to a few of the other offerings that look either too conservative or simply riced out and sounding tinny as heck.