Evening all.
After a while being a voyeur, I decided I'd better register as I'm at my wits end.

Can anyone tell me what this noise is? https://streamable.com/ttnl1t
The first noise about 12 seconds in is me releasing the handbrake.
The noise in question is about 18 seconds.

I was originally told it was the vacuum pump, so got that swapped out. No change.
Then I thought it might be the little valve on the side of the vacuum pump. Swapped that out last week, but it's still the same.
Only seems to happen when I'm using the brakes when in EV mode. Then again, maybe I just can't hear it when the engine is running.

Any ideas?