I'm not sure I follow this completely. The faint noises you'd miss without headphones...what faint noises are these? Are you talking about the change in threshold, or the faint hum over a deep target in all-metal mode? (true all-metal...where all you get is the single tone/threshold noise over targets).
I use a fisher CZ7, and there is no option...I must use headphones as this unit does not have a speaker. I just use walkman type headphones because of comfort, heat, weight, and so that I can hear sounds in my environment as well. I hunt in disc mode (3 tones, low for iron, medium for aluminum/gold/nickel, and high for copper/silver/clad). I haven't ever heard a very faint "beep" in this mode. So, are there beeps I'm missing? Or are we just talking about all metal mode here?
Not to carry this too far off topic, but while I hit on the subject... Does anyone still hunt in the old-fashioned all metal mode anymore? I've never done it, and can't see how. When I go to that mode on my machine, I hear noises all over. I guess there's so much junk in the ground around here. In one sweep, I can be sure to hear 3 to 15 targets in that mode in most any place I hunt. How do you determine which ones are coins or something worth digging? I understand that there is more depth gained from the machine in that mode, but if I can't discern anything from the noises, it's not doing me any good. If there is, however, a way to do this, I would love to know! I am hunting some sites where there are very old coins, but they are deep and it takes a lot of work and just as much luck to get a beep off of one.