The review on e46f references those clamps as leak points and the OP had them welded...could be the same thing.
"The first was the Torca clamps inability to completely close the gaps in the female ends of the pipes. This caused six little “holes” where exhaust would leak. The problem was compounded by moisture in the system (normal in the NW) sputtering out of the holes at idle. It didn’t affect the performance; it was simply an annoyance to me. I had the boys over @ Portland Muffler weld up the entire system and it fixed the problem. "
http://forum.e46fanatics.com/showthread.php?t=261194