I just got an EHX Germanium Big Muff and this is a TON of hum on the overdrive side. Tweeking the bias knob quietens it somewhat. No difference whether run alone, in a chain, off power supply or off battery. Is this a defect or what? I am a EHX loyal customer (1st gen. POG, Memory Man, Holy Grail), should I return this or is it to be expected?