The packing will do the majority of its settling early but will continue to settle for the life of the muffler and never reaches a final state. Most modern internal combustion engines will produce approx. 1 gal of water for each gal of gasoline burned. The combination of corrosive exhaust gases along with condensate is a recipe for corrosion and this begins to attack the mufflers and their packing materials as soon as the engine is started up for the first time with its shiny new cans. Then you have heat cycling, material deposits from the exhaust stream, and sonic deterioration to add into the mix.
Mufflers will nearly always get louder over time when actually measured with testing equipment. This isn't exactly a secret.
2012 E92 Space Grey with fox red/black/black, comp, premium, DCT, premium sound, sirius, heated seats.