It's a repetitive thumping sound in the audio.
Could be a higher frequency, as in a buzz.
Often associated with poor grounding, poor bypassing, or a battery at the end of life.
Could also be caused by RF feedback, as with a transmitter or other high power device.
I don't fully agree
with this Wikipedia description, but it's something to go on.
I can't think of anything in your install, other than cabling, or AC wiring/grounding that could cause it.
Can you take that receiver to a different room / house, and try it there?
I wouldn't think the receiver was at fault , as in bad bypass caps...