intermittent audio pop (mac studio m2, bitwig)

[synthique]

setup: Mac Studio M2, Bitwig 5.3+, SSL 12 USB inteface, Arturia AudioFuse X8 (in) ADAT
The SSL12 has 4 analog ins + 8 ins via ADAT.
I'm getting an intermittent pop that sounds like a bad cable or timing sync issue. This happens without having Bitwig running; I can run SSL 360 mixer software and the same noise happens. During recording the noise is recorded exactly as I hear it. It's impossible to get through a minute or two of recording without at least one pop being recorded. Looking at the waveform of the recording, zoomed into the sample level, the signal's phase switches at the instant of the pop.
I've had lots of analog gear plugged into this setup but I'm only hearing this now that I've plugged the Moog Matriarch into the 7/8 channel of the ADAT interface.
I'm going to switch off the ADAT interface and try the Matriarch through the SSL's analog ins to see if it's something to do with ADAT sync.

[synthique]

It was the SSL 12's setup. With an ADAT + optical link, the sync has to be changed from "Internal" to "ADAT" in order to get the word clock from the ADAT interface.