TV sound bar making odd noise when off?

So I've got this shitty vizio tv and sound bar. Don't really use the sound bar much but I fell asleep on the couch last night, woke up to take a piss and heard the most peculiar sound. It was high pitched as hell. Kind of like when dust would build up on the old tube tv's but it wasn't a constant tone. It sounded like the noise you hear on shortwave sometimes kinda morse mixed with fax machine noise. It took me a while to locate it but unplugged and all was good.

No wonder my sleep is shitty at times.