What is this noise?

I’m in a soundproof booth and have no fans/furnace/AC/Washer/Dryer/ or dishwasher running. My booth is also in an underground basement. However I cannot determine the source of this noise. Periodically it disappears but I cannot find out why? Please advise

It looks like a low hum, and possibly a crunch sound at around 16 seconds. Difficult to say more than that without hearing it.

Actually, it appears to have been my powered USB hub. Thank for your reply!

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