Songs randomly go silent when using iTunes (Music) with Airplay.

My iMac is connected to an audio receiver and a couple different speakers via Airplay. Pretty basic setup. Various songs just go silent. This is random; can vary between one in every 10 or 20 songs. The song looks like it's playing — the progress bar and time is moving, but nothing is coming out of my speakers. Then the next song or next few songs will play normally. If I turn off the Airplay speakers the sound comes on thru the iMac speakers. But as soon as I click one of them back on, nada. This has only happened when using Music/iTunes. I've checked the network connection and all the other obvious stuff, yadda, yadda. I have seen this mentioned in older posts here but with no resolution.