Hey Clark,
It sounds like you want to know what coin hits sound like. It also sounds like you may be trying to detect in trashy ground. If you switch to Mike Moutray's settings, I can help you. Those are the settings I am familiar with. Mike Moutray's settings are found on this forum and on http://groups.msn.com/MinelabExplorerXSusers site.
You need to make sure the threshold sound is turned on so you can hear it.
In trashy areas, I set my Sensitivity on manual. Then I lower it until I can get a little bit of intermittant threshold return in between some targets. You do not want your threshold to be gone all of the time. If it is gone all of the time, you are probably getting a depth of 1". If all you hear is silence, that means that the trash targets that you are discriminating out are distracting your search coil from deeper coins. If you turn your sensitivity down to 15, the area of influence of the shallow trash targets decreases and helps you to look in between targets more and get better depth. In super trashy areas, you need to double sweep 4" lengths with little quick sweeps. If you don't, you will pass over coins.
You need to do some air tests and listen to coins by themselves. Place different coins on clean ground and sweep over them at different altitudes. You will be able to hear the difference between shallow and deeper coin hits.
Gotta Go,
Mike