Very interesting, Brad. In my particular case, this was only for a minute or two -- once near the beginning of my hunt, and once near the end; in between, it was just fine. Had never experienced anything like it. I was sure the detector was toast.
One other thing I will bring up though, that just MIGHT have something to do with it...deano, does your F2 have a screw-in type connector on the control box for the coil wire? Mine does; aside from these two brief machine "freak outs," I had a case where my machine stopped working properly (same hunt, same day). It was reading weird, so I stuck my boot out, and the metal eyelets were reading "iron." I thought NO WAY. So I pulled out a quarter, tossed it in the grass, and it gave a digital "15" read out, and iron tone. I said "what the heck??" I then checked the screw-in connector. It was a little loose; tightened it up, ran back over the quarter, and it was all back to normal. So, I don't know if the "loose connection" may have been part of the "interference" issue; I can't remember if I tightened the coil wire before or after that last case of the machine going ballistic, but it's at least POSSIBLE that I tightened it AFTER both instances of that "interference-type freak out," and thus that the loose coil wire could have been related to the issue...
Steve