I had the same thing today. I hunt in normal coin mode and when I get the ding ding, swap to Pro zero to try and get an idea about size and depth. When I swapped to Pro zero it was only a faint signal and I thought a small piece of old iron, copper wire etc. I started digging a hole about two to three inches down, and using the Pro pointer, but no reading. Ran the AT Pro over hole again and still a faint signal. Kept digging down about another four inches and found a 1951 sixpence. It's a hard call I think, do you give up thinking its just trash, or my way of thinking, if you haven't found it in the first two to three inches and the Pro pointer doesn't pick it up but the detector does, keep digging.