I bought myself a brand new mustang pj and noticed something very strange. With the volume on it hisses,ok maybe the shielding is not done very well but when I turn the volume all the way down I get a humming noise. The same noise as if you are leaving your cord unplugged on the ground. Checked the amp by trying another bass,switched cords,... But it's the mustang. A bass that hums with the volume all the way down!!!!?????? Anybody who knows what could cause this issue?