You can use a Mechanic Stethoscope or as I do use a cut off Broom stick to listen to see if you can locate where the sound is. Being careful not to hit any moving parts place one end on the supspected part and your ear on the other end. Move it around until you think you hear were the sound is the loudest.
To inspect the parts of the Vacuum Pump that would make noise you need to remove it from the engine.

Some more questions.
When you look at your Oil Pressure Gauge what type of readings are you getting and does the Needle on the gauge stay steady or pulsate?
Do you have the White Smoke all of the time or only when you start up?
Have you ever looked under the car at the Motor Mounts to see if that was the problem (or you can listen with that Broom Stick)?

Depending on the type or the Air Filter Housing that you have on your Car they can vibrate against the manifold or the Air Filter Housing rubber Bushings or the Air Filter Housing Bracket can be broken.

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84 300D, 82 Volvo 244Gl Diesel

listen to vac pump, and then if thats not it I'd check the valves- one could be loose and hitting a piston.
I'd not drive it until you at least narrow it down.

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.

The oil pressure gauge is reading pretty normal, goes to three when you give it some gas and sticking around 2. The white smoke is all the time. I'm pretty sure the air filter housing and brackets are just fine, I'll check but I doubt that's it.

is it 2bar right after start-up or at full operating temp? That could make a big difference and indicate a comprimised bearing.

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