Check the bottom of the distributor shaft to see if the flat drive tang for the oil pump has sheared off. With the noises, it's more likely an internal failure in the pump. Getting the oil pan off might be a challenge. On the smaller trucks, supporting the frame on jack stands and letting the axle hang down gives a few inches more pan clearance- - - -not sure if that will be necessary on a big rig.

Another possibility is that the oil pickup screen has come adrift and the crankshaft is hitting it.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!