The way I hunt in all metals (almost any machine) is to crank the sensitivity (gain) 'way down, adjust threshold hum to a comfortable background listening level, and then crank the sensitivity/gain control up until the background noise is clearly audible in the hum but not to where it starts to get choppy.
Then, of course, ground balance. If the ground turns out to be too noisy, then crank sensitivity/gain back down until the ground noise is tolerable and is not driving the background hum silent. And pay close attention to maintaining good ground balance while you search.
If either the threshold control setting or the signal noise pushes the background (no target) sound down into the silent region, you can be walking over weak signal targets and not hear them. This is why all metals searching is normally done with a continuous background hum.
