I noticed that the J-Bass I have ( MIA) has a hum that comes through the amp when either one of the pickup are turned to less than full, with the tone control set to full. The hum will go away, if I turn one or both volume controls to full on, or turn the tone control off. Does anyone have an experience with this problem? I have a SWR WM 12 and it does not have the problem with a P-Bass I have. Checked to make sure no outside interference is the cause. Thanks.