Sounds like you are using an F75 LTD. I use the standard F75. Regardless, it sounds like you either have a lot electrical interference where you are or you have a bad coil. I normally run mine with Sensitivity 88 to 94, Disc 4 to 12, DE Mode, Notch 1, and 2F Tones. Sometimes mine gets real chattery with the numbers jumping all around. When this happens I first try changing frequencies. If that doesn't work, I do a reset on the machine. If you are still having these problems, I would send the machine back. I have had mine for 6 years now and I love it, but it has been back to the factory 3 times!