I have a Garrett AT PRO and I'm having an issue with it. I've returned it to Garrett numerous times to no avail. They sent me a new detector but the issue persists. The issue is that when detecting in a field if there is a tiny, single, taller sprig sticking up above the grass and I touch the sprig with the coil, I get a coin signal. However, there is nothing there. This makes it very difficult to hunt. On the beach it does the same thing when I accidentally touch a mound of sand. Has anyone else had this issue? Any ideas on what might be causing this? Any suggestions are appreciated. Thanks.