I have a TLM-103 that I recently purchased for recording. It works fine in most cases - but for female vocalists, it has a strange harmonic that creeps in at certain frequencies/level. It sounds like it's 2-3 octaves below her singing voice. I had to put a notch filter in the track to salvage the recording - this of course destroyed the quality. I have other mic's I've tried with no problem. I use a pop screen and she is about 8-10 inches front the mic.
What could be the problem?