Rod and main bearing time?

[atancreti]

Hello,
Looks like I have some work ahead of me....
Its a 3.9L 1995 D I
The other day I noticed my engine when I gave it gas started making this vrmmmmmmmmm sound. Its a very faint sound. Not really a knock or tick. Of course engines do make sound when they speed up in rpms.... But this is deep. I had a friend do it while I was directly under the oil pan and I would say its coming directly from above the oil pan.
Who can offer some advice on doing this?
Do I need to pull the engine to do the rod and main bearings?
What else should I know.

[I Leak Oil]

Perhaps it's the viscous unit on the fan? Waterpump? Alternator?

[Roverx]

Take a piece of 3/8" rubber hose and use it as a stethoscope. Should be able to figure out where the noise is coming from.

[atancreti]

Great suggestions! I will get some rubber hose and start listening! Wonder what would happen if I took the belt off the engine... Just to run it for a couple of minutes to see if the sound is still there when the fan, alternator, and water pump aren't running.... hmmm?

[ColoDisco]

I had a viscous clutch sieze up and make that same noise. Replaced it with the chevy express viscous clutch mod. Worked great ever since. Does still make the noise but you can tell it is not siezed as after I replaced it I no longer get the noise while driving down the road.