After connecting the speaker cable between the speakers and the amplifier, I can hear a tiny 'hiss' or 'humm' sound coming out from my left and right speaker (I only have stereo) once I switch on the power of the amplifier. You can hear it when you stay close to the speaker within 1 foot.

I've tried to turn down the volumn to minimum, I can still hear the sound. Obviously, the sound is gone (covered) when I start playing music.

Do you have any idea? Thanks for your time.