Glasspacks can have a so called break in period. I believe that's what you're referring to. Glass packs will get louder over the first 6 months or so that you own them. I'm not sure whether or not magnapacks are glasspacks or not. I assumed they were more resonators like lm's.
Engine/Drivetrain: SCT iTSX with BAMA 91 Race Tune, Airaid CAI, JBA O/R H-Pipe, SLP Power-Flo Catback, Exedy Stage 2 Clutch, Exedy Lightweight Flywheel
Suspension: H&R SuperSport Springs, KYB Shocks & Struts