I was dealing with this quagmire when I first started using my Safari a few weeks ago. When that hum sound stops over a target it's something you are scrimming out, sometimes as iron degrades it will cause you to get #'s (34, 36, 38 etc) in that area. But I bet when this happens the numbers aren't constant and you're not a getting a good clean signal. I was relying solely on the screen and when I heard something scrim out but got a few quick signals in the high 30's I dug anyway and it was always iron. I just hated to pass over them because maybe it was a good coin next to a hunk of garbagio, but it always turned out to be garbage. But after digging some really nice coins at the 7,8 and 9 inch depth there has been no mistaking the good clean signal, and the #'s hold fairly constant and don't bounce all over the map. The last 2 outings when I hit those iffy all over the map signals I don't bother wasting 10-15 minutes digging, I move on and look for solid signals. I may be passing up something good who knows, but I've been far more successful in my hunts operating this way. Some folks prefer to dig everything, I just get tired of working a hole that ends up producing junk. What also helped me is that my friend I go MD'ing with has a minelab excalibur and we cross reference each others targets before digging. Almost 99% of those iffy all over the map targets I run across I have him take a quick swing if he's nearby and almost always he has the same opinion, just some iron. The best thing to do is cut a plug and put a coin down at about 6" then swing it, then put it on edge at the same depth and see what you get for #'s and a tone.