Hi!
My D2 is running great! But all of a sudden I'm hearing intermittent sound coming from the front of the engine. Maybe right beneath it.
Sounds like rocks rattling around... and like something is about to break away. It doesn't affect the engine running at all. Engine isn't knocking... and is smooth as normal.
The belt looks smooth and I don't see anything wobble along that system.
Any thoughts?
Thanks!!

 

My money was going to be on one of the pulleys. Possibly could be the water pump too. If you just put a wrench and pull the the belt, you can check all of it.

 

I agree with longtallsally. Put a 15mm socket on that belt tensioner and release the belt from at least one pully. No need to remove the belt completely. Then, grab every pully and check for play. Grab the fan and check for any play in the water pump shaft. Replace anything that is at all loose. There are horror stories about what can happen if the water pump bearing fails to the point of the water pump coming apart. The fan flying around the engine compartment results in carnage.

 

Thanks for all the suggestions. Here is a video of the problem.
It has to be the water pump shaft. I saw a slight wobble in the water pump pulley. I didn't remove the fan clutch to check with when I took off the belt. But has to be the problem.
Water is flowing fine and engine isn't over heating though.
Hoping to drive it 10 miles to the shop? Hope to make it.

 

Video

 

A water pump with a failing bearing will circulate coolant just fine. Until it doesn't.

Any evidence of coolant leaking from the water pump weep hole? How many miles on the truck?

The water pump in my DII failed at ~178,000 miles. I replaced it with an Airtex 9369 ($72 from an Amazon seller).