i replaced a cheap sub cable with a mediabridge cable the other day and it made that boom noise also, although not too loud. i forgot to unplug the power cord. anyhow my f12 is fine.
My whole system was unplugged. it made the noise when I turned the power back on the surge protector. It still works But I would like to know why that noise happens when the power gets turned on and when I plug the rca in . The receiver was off when I plugged it in.