I have just picked up a Pro-197 scanner and I have my local system programmed in it (Central Maryland Radio Committe 700 MHZ APCO-25) the radio will scan and stop on a channel, I can see that it is receiving something but I cannot hear anything. The signal master jumps around (it doesn’t stay steady on a certain reading) I know the speaker works, the radio will revive stations just fine when I turn the volume up I just hear a light hissing sound.