This ended up being the answer, I think. I played around and found a random setting that I could change but there was no indication on the screen as to what I was changing. Don't have it in front of me but it wasn't sensitivity or volume and I think maybe it ranged from 0 - 20. If I have it set to literally anything other than 0 it produces the constant whine.
The thing is I couldn't seem to figure out based on the manual what threshold even is or does, all I know is the detector is almost unusable if it isn't at 0.
Also, maybe I'm just used to a less sensitive detector (coming from bounty hunter tracker iv), but I can't set it to much more than like 4/8 sensitivity or it beeps in midair.
I find that beach mode is the only tolerable setting, even though I don't live anywhere near the beach and never had a problem before with hot rocks or weird soil. Coin mode is not... Trustworthy.
Finally it seems to think most hits are a "silver dollar" for some reason, so I pretty much have to ignore the discrimination.
All in all I have to say I'm quite disappointed and spend most of my time fighting with the detector trying to get it to behave and very little time actually swinging it.