It's a fix it ticket. No big deal. And the cop dropped his other ticket because the car is so loud it could hardly be ignored. Sure he's been looking for you--you and anyone else that sticks out in a crowd. (Number on rule of not getting picked off is not to stand out....)
If this thing can meet noise regs for CA, just go to the referee station (as QS pointed out) and get it signed off. If not, fix it, and get it signed off. No different than a fix it for tint, or front plates, or whatever.