i have a 5.1 surround system that is playing up. it will be playing at normal volume then gets really quiet, then after an unspecified time returns to normal, or can change constantly quieter then louder. I have managed to figure out it is something in the electronics of the amplifier rather than the volume knob or the input. i think this because if i turn the volume up high it still does the same and doesnt crackle ruling out the volume knob. if i plug it into another device it still does the same thing. my question is. how do i track down the faulty component?