So I bought my 744 n.a. with 108k miles. It needed a new muffler. The previous owner gave me a lot of the old maintenance records. Among these was a receipt for a muffler-- it said guaranteed, free replacement. This place wasn't even Midas, it was worse (if that's even possible), a real hack place. But the new muffler was free, so what the hell. It gave out a wee bit later, in about 25k miles (I forget exactly), and I did the same thing. This next one lasted over 30k.

When that one finally started making too much noise-- it got a hole in it-- I decided to get a good one, so I bought the Walker/Starla from FCPGroton.The old crap had all been welded together (though I used clamps when I had a new cat put in), but I still needed to go to a shop to cut off the axle-pipe-to-rear-muffler weld. The new one was put in, but I stupidly let them re-weld to the axle pipe, though I did make them use a clamp to the tailpipe.

Anyway, the rear muffler (yes, it's the rear muffler, not the cat or front muffler) now rattles loudly occasionally (it seems to come and go in phases). It's only been in the car 10k miles! No holes this time, it's internal.

I drive mostly highway miles, by the way.

so,
1) has anyone else had Walker/Starla mufflers die this soon?
2) is there something I'm doing that kills mufflers fast?
3) should I be suspicious that my front muffler has now outlived 3 rear mufflers?