Allnic H-3000 hum when mute button engaged.

Hello Goner,
I have just purchased this wonderful phono preamp used. The unit is running perfectly and quietly. There is only one problem, that is when the mute button is engaged, my speakers hum badly on bith sides. Anyone got any idea on what happens. Also, when the button engaged and disengaged, it produce the pop sound. Is it the possibility that the mute button is malfunctioning? Can a simple deoxit fix it?
 Thanks 
Calvin