Volvo 850 engine whine

Hello! I have a 96 Volvo 850 and recently I’ve noticed a weird whine when I turn the engine off. This doesn’t happen every time and there seems to be no particular pattern when it does happen. It whines anywhere from 5-10 seconds (it sounds like an air raid siren from very very far away). Any ideas as to what this might be? It’s not driving any differently.

Possibly a vacuum leak or perhaps a coolant hose collapsing.

Maybe 20 other things too. That’s a tough one.