GoodMorning everyone my names Eric I recently bought a 94 940 for 1,000 with about 245,000 miles single owner and all original paper work with stickers and maintenance records up until April of this year. Just recently it started making a whirling noise yesterday and it was extremely loud and can be heard from the cab today I started her up and very minimal noise it can barely be heard. Here is a MP3 at about 8secs is when the noise is at its loudest. I read on the forums that it might be a belt or a pulley but I don’t know what a pulley is this is my first time being a diy cool guy. anything helps thank you for your time and patience

 

Sounds fairly normal, however you can use long ratchet extension like a stethoscope. I use my long 1/4" one, place one end in your ear (not too far) and then touch the other end to various moving engine accessories. If you hear a change in pitch, it may be the accessory bearings. The same method applies to noisy valve trains.
Obviously, be careful and keep the rest of your body away from moving parts. This method may help you identify the source of the noise.

 

A simple test to determine the source is to spray a little water on the inside of each belt separately, while the engine is running. A loose belt will temporarily gain traction from the water. If the noise stops when a certain belt is sprayed try tightening that belt. A common noise is a worn out water pump. Mine did it. If the spraying doesn't work try removing the water pump belt. But don't run it for too long since you're not circulating water with the belt off.