Hello everyone. I recently picked up a "like new " idx pro from a widow. She told me her husband never used it. First thing I did was put fresh batteries in it. I am having some issues with it. On an air test with a one Troy ounce silver coin I can barely pick it up at 4 inches. I am using quality headphones. My plan was to get a 15 inch coil an search for deeper objects. Anyone have any ideas? Could it be a bad coil? There seems to be a fairly loud thresh hold noise when the coil is away from everything. And when I disconnect the coil wire from the box the noise goes away. Any help would be greatly appreciated. I would like to get the Mr. Bill mods done to it. And iam trying to save money and avoid sending it to whites first. Thank you in advance.