have this audible hum when nothing connected, irrespective of input selection. When music is playing it's masked but definitely present when not. Both channels. With an audio tester, I confirmed this same hum on pins 16/18 of the power supply board. All DC output voltages from board match schematic, though the AC one is a little higher (8.xvac) Some of the larger caps related to the right hand circuit had more metal top showing then i would expect, though they tested fine on a in circuit esr meter. I replaced them all anyway (everything 100uf and higher on right side of diagram, see below) no improvement. This includes the 330ufs that people hadve changed that fixed hum - but not for me. Should something else in that circuit be looked at/measured, or are the large 15000uf filter capacitors suspect? Hate to change them unless absolutely sure, given the cost.