i have found that sometimes amps in subwoofer cause a hum.. this MAY be normal. I'd call or write to ML and find out.
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Outlaw Audio 990 pre amp
Adire Audio sub (SVS 12.2 driver)
CAL Alpha tube DAC
Parasound P/HP-850 2 CH pre
Pioneer PL-530 TT
Polk Audio SDA 2B
NAD 2600A amp
Danger Boy here