fnkcow and I had the same exact issue (left side, low frequency driver) occur after about 2 weeks of ownership back in September. My replacement pair hasn't skipped a beat the past couple months so I think there may have been a bad batch.
I haven't had too much of an urge to try anything new thanks to ericp10 who has kept the M200 in high regard even after trying the newest and latest IEMs out there. That, and the M200 sounds oh so good.
Edited by PeterDLai - 12/27/13 at 8:08pm