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Setup is 13" MBP 2019, running 10.14.6. It's connected to a 24" Dell monitor via AmazonBasics USB 3.1 Type-C HDMI Multiport Adapter, sound from monitor aux out into speakers.
When sound is on external monitor (type DisplayPort in sound settings) I have periodic sound cuts, like momentary blips. The interesting thing is that this happens on a 14/56 second periods ie. a cut in 14s, then next one in another 56s, next in another 14s and so on.