Try new batteries first and confirm with headphones and try different programs - Hopefully that works. I had two F22 machines the first one went crazy after about a week and the 2nd one the Pinpoint button moved (came unglued) after about the first month.
Best feature on that machine is you can turn sensitivity down to about 2 or 3 and get right next to playground equipment. I have found quarters within a few inches of big steel poles using that method and under metal slides.