DIAGNOSIS: That pop is usually an electrical surge or discharge in the audio signal path, often triggered by the TV's internal amp turning on/off or a bad HDMI-CEC command.
FIX: The most reliable fix is to break the CEC control chain for audio. In your TV settings, find the CEC control option (often called Simplink, Anynet+, BRAVIA Sync, etc.) and turn it OFF *just* for the system audio control. You'll use the Sonos app for volume instead. This stops the TV from sending rogue power signals to the Arc.
IF THAT DIDN'T WORK: It could be a ground loop or power issue. Plug both your TV and the Arc into the same power strip or outlet if they aren't already. If they're on different circuits, the slight voltage difference can cause audible pops.
HEADS UP: If the pop happens consistently when a specific device (like a cable box or game console) switches resolution or activates HDR, the issue is likely upstream. Try inserting an HDMI audio extractor or a different HDMI switch between that device and the TV to clean the signal.