Drop the sensitivity down a notch or two if you are hunting at full sens... I think you are experencing a little falsing. This can occur when you swing too fast, raise the coil during the sweep, hit a wet weed... Lots of reasons. Slow down and make your swing from side to side take about 3 or 4 seconds. Keep the coil as level as possible during the entire swing. Listen for the faint tones in Pro mode. Slowing down makes that easier.
Also, once you THINK you have a good target, approach it from another angle, (90 degrees) and see if you get a signal, if so there is probably something there.
Once you have found a target with the AT Pro, if it's fairly shallow, you can take the ProPointer, turn it on and put the tip to the ground and try to locate the target before you dig to help you recover it quicker with less digging. The ProPointer has a range of about 2" on a coin.
ALL OF THE ABOVE COMES FROM ALMOST 2 YEARS EXPERENCE WITH THE AT-PRO & ProPointer.