Broken tinsel lead on MM100... Help!

Systems

Hey, I've been running two MM100's in my pickup for about a month now. I'm still running them on my Lanzar Vibe 1200D at two ohms, which is about 800 watts rms total. About two weeks ago, one of the subs stopped working. I took it out of the box, and the tinsel lead separated from the negative post. The lead seems to be way too short. So I had my dealer solder it back on for me and it worked again for about 30 minutes, then broke off completely. My other sub has been fine. I'm just wondering what could have caused this? Could an air leak in my box have anything to do with it? Anyway, my dealer is already shipping it back to you guys to warranty it, I was just wondering about what could cause that. Thanks.