Misfiring and muffler problem

[dd4321]

Just recently done a muffler checkup as my R33 GTST has been making rattling noises in certain RPM (around 1500 - 3000rpms). Found out that the middle muffler is stuffed big time... the internals have been shredded. My HKS Hiper catback muffler is in fact less than 1 year old.... what the??? Brought the car to HiTech muffler and get the middle muffler replaced for $320 (ouch). I was told that the muffler was destroyed because my car often misfires. Is this right?

Strange though after replacing the middle muffler, the car does not misfire anymore (although rarely it still does). Any correlation between misifiring and damaging muffler? I would expect my cat converter to get stuffed before any damage to middle muffler. In fact the cat converter is still looking healthy.

Any opitions appreciated!

D