Hi, lemme preface this;
I had the OEM exhaust and it was a bit too quiet for my liking, could barely hear it over the engine (G35 Coupe '04, minor mods). So I decided to get catbacks and keep my OEM cats cuz California. I bought a HKS replica that was on a 370z, took it to a shop, got it installed with the extensions and all is sealed and well.
I take off and immediately think "oh sh*t", the exhaust is STUPID LOUD, At 2k RPM I need to scream to be heard over the phone, and its a manual so no bueno.
I go back to the shop and say I want to quiet it down and what can we do, they are going crazy trying to lockup because of a protest today (Anaheim for those who are wondering) and they said come back tomorrow to install the OEM one as they cant do anything to quiet it down.
What can I do to quiet it down as my phone read over 130db (law says 100 db max ). And if no solution, what exhaust do you recommend that is just a bit louder than stock but deeper.
Thank you everyone!

I put a washer in between my mid-pipe and muffler flange. Just enough to make sure the flanges leave a slight gap and dont mate all the way. Sounds a bit deeper but not too loud. Some people have told me it sounds like a nismo exhaust. Try it, I think youll be happy with it.

The HKS rep is one of the loudest exhaust on the market due to the design. Any true dual is going to be loud though, even the Fast Intentions Traditional was a bit too loud for my tastes.

It depends on how badly you want that extra 10whp, to me it wasn't worth it so I kept the stock OEM coupe exhaust and put the FI resonated HFCs and it's exactly what I was looking for.

I'd say your options are to add a resonator the HKS or do a resonator delete from your stock catback.

Swap out the resonator with a Vibrant Ultra Quiet resonator. Really knocked down the drone on the Tanabe exhaust I had.

I got rid of the HKS rep already but it had a res and was still stupid loud
Idk about a res delete on the stock one since id rather not have a drone going on
I live in Cali so HFCs are a big no no
Ill try this soon since its a harmless experiment.
Thanks for all the advice guys

Also I got a question. Some people are saying that with washer mod you loose hp some even say 15hp. Is there any truth to that? Because it doesnt make any sense to me unless you say im loosing back pressure