If I may: The Ground Balance on the F4 only works in All Metal (not All Metal Discriminate) mode. Since the pinpoint function is also All Metal, you do need to ground balance the F4. I've noticed that when my F4 is not properly GB'd, it will sing/hum/chatter in pinpoint even when not over a target. I know it says this in the manual, but make certain that there's nothing metallic under the coil (I use all metal disc) before you start making adjustments to the GB. Makes it kind of hard to locate your target when everything sounds the same.