I've been hunting my se in ferrous all metal for 6 months. there is a constant song of low tones not really targets but ground noise as long as the detector is moving. it seem like i only here a threshold when its still. good targets chime through the noise and I'm finding stuff is this the way it should be. am i missing targets in the noise does the detector recover fast enough. when i add a little iron mask it nulls a lot even when sensitivity is down to 20