So get hold of the plant manager and hassle the fuck out of them until they help you.

Dude, this is fucking painful. You're only solution is to get it turned off, covering it up or trying various methods of redirecting the air are not going to work, as explained multiple times, despite how much you perceive that to be the easier option. You've three options:

1: live with the noise

2: move premises

3: find the person who can turn it off, and get them to turn it off.

Nothing else will work. I suspect that options 1 and 2 are actually impossible which leaves you with 3, which might be difficult but is at least achievable. Going round in circles because you don't like the answer is fucking pointless.