What's the BUZZ between songs with iTunes and DAC

I am getting a really loud electronic crackle and buzz coming through my Airport Express when there is no signal (music playing), such as between songs and/or if I pause the playback in itunes. What's the buzz about?

I know I read about this in a discussion here but for the life of me, I cannot find it now. (Maybe it was deleted like so many threads that disappear these days)

Here's my set-up:
iTunes to Airport Express to Monarchy DIP (via optical) to digital in jack in CDP Opus 21 (via digital coax).

Also, sometimes when I begin play, the sound is degraded to an am-radio quality signal but if I pause and restart it comes back to high quality.

Any thoughts or help would be appreciated.
If you remove the Monarchy and run the Airport Express directly into the Opus doe the buzz and crackle persist? It sounds like your D/A is losing signal lock.
I need the Monarchy to convert the optical signal from the Express into a digital coax electronic signal for the input on the Opus. Otherwise I would not even have the Monarchy.