I've had my catback for about 6 yrs, no real harsh environments as far as weather, road salt etc..etc. My muffler has started to rust from the inside out and its supposed to be aluminized. Started with two pin sized hole with small drops of water/condensation, not the flanges where my tail pipes connected are rotting away. Any thoughts?

 

Aluminum is your cathodic protection, it works by being
consumed and when it's done it's done. Question is how
thick is the aluminum layer and how consistent the
coverage. One pinhole and there's your corrosion cell
in miniature. Every day you blow a whole lot of acid
loaded (NOx) steam through it.