... and loose output RCA god, this preamp sounds amazing (paired with a matching M-60). But - this weird thing happens where random channels (sometimes both) start this woofer pumping thing. When this starts happening, the volume adjustment makes no difference, but the Loudness knob definitely does, it increases the amplitude of the pumping to where the sound definitely becomes audible. If I don't touch the loudness knob all is fine - but the meters on the amp keep a steady noise floor, without the meters I probably would never notice the thing So - what would cause this issue and how do I go about troubleshooting it ? I tried cleaning the volume pots with deoxit (through the 3 holes in plastic housing) but the issue prevails - I cleaned up some glue mess around the voltage transistors (see before shots below). DC offset: R:2.1mV; L: 1.9mV cheers!