I have a Foreplay III and something has gone wrong with the sweet Whisper volume control for my left channel. It is fine on the first two settings, but when I turn to the others a loud pop is heard and once set in the new position a loud humming noise comes from the speaker. It seems that the switch is sensitive to touch. If I remove the knob, I can recreate the problem by just tapping the top of the switch. Any advice? Should I just buy another set? Thank you in advance.