'98 E36 - Loud Noise From Engine Compartment

I have a 1998 e36 convertible.

Saturday, I was just coming home and just after turning into my drive, a very loud noise started coming from the engine area. There is no metal sound... it is just a very loud almost vacuum cleaner noise every time the car is on.

Any ideas or suggestions?

This engine was just replaced 5 months ago with a used engine.

Check for a vacuum leak somewhere. Maybe a leaky air inlet elbow or something. people use a stethascope to find leak like that but if lts loud enough you should be able to pin point where the leak is, if it's perhaps a leak.