I know that we should never say never. But I've never found a US coin that would bounce between the conductive (positive) and the ferrous (negative) TID numbers. If I get a target that does bounce between the high positives and the low negatives, I'd almost bet the farm that it is deep iron or multiple targets. I use Prospecting to determine if there are more than one target. My theory on a mixture of negative and positive TID numbers is that discrimination is circular instead of linear. By that I mean that the most ferrous target is adjacent to the most conductive target, on the TID scale. Since the TID stops at -8 and +48, I'd have to guess that some targets are either more conductive, or more ferrous than the scale allows. And in my opinion, deep iron (and iron oxide) meets that criteria. One suggestion I might give would be to try the multiple tone mode. Those bouncing numbers you are getting will also produce wavering tones. If you wiggle the coil over that target and slowly drag the coil toward you, those low tones will become very apparent and save you a lot of digging!
The volume of your menu option tones is based on where you have set the volume of your detector. The only way to make them "softer" is to reduce that volume or the volume of your headphones. If your hearing is good enough for those tones to be a problem, I'd might wonder if you have your threshold set too high??? Take the term Threshold literally. Anything more than a barely audible sound might not be allowing you maximum performance.
The "default" start up mode for the X-70 is the last pattern mode you used. It can be Pattern 1, Pattern 2 or Pattern 3, depending on which one you used last. Just in case I forget to move to all metal when I first turn it on, I set up Pattern 3 with zero discrimination and all the same settings that I typically use in all metal. That way, if I forget to switch to all metal, when it starts up in Pattern 3, it will mirror my all metal mode settings.
The sensitivity settings for Prospect mode and C/T are made and saved separately. However, your sensitivity settings (last used) will be there when you start up the detector the next time. HH Randy