MY SON WANTED TO BUY A ULTRA GTA 350 USED . WHEN TRYING TO SCAN THE GROUND IT JUST CRACKELS INSTEAD OF ANY TYPE OF TONE. WE HAVE DID AN AIR TEST AND IT HAS TONES FOR COINS. WE ALSO HAVE AN ACE 250 AND THAT IS JUST AWSOME , MY SON AND DAUGHTER BOTH LOVE IT. ANY HELP WITH THE 350 GREATLY APPRECIATED.THANKS CORY