If you look closely at the water pump pulley it's moving quite a bit. I'd say that's the cause of the noise. It's also transferring the harmonics to the tensioner pulley.

 

Just a thought... Check for a blown exhaust manifold gasket, or head gasket. When you shut the engine off, it sounds like something is decompressing.

 

The fan is fine. The reason it looks odd is because the camera is prolly recording around 20-30FPS. That fan is spinning wayyyy faster than the camera can "see".

 

Your fan looks fine to me.

It looks "wonky", as another posted, because of the low frame rate and the viscous fan is not evenly spaced blades. It has a grouping of 3 and a grouping of 2 if you look closely.

I'd wager the water pump impeller is shot and scraping, or you've destroyed a bearing in one of the pulleys. It's also possible that bushing in the idler pulley is cattywampused.

 

Thanks guys, I will update this tomorrow. I'll try to tear the belt off quick tonight and manually rotate the accessories and see which is the culprit, even though it's 10deg out.

 

I can tell immediately what the problem is by sound. In the end of the video there's an obvious clue of what the issue is. (At least I thought so initially- not sure now) When you killed the motor, the modulator fan kept free-wheeling for a very long time. In addition to that clue, there's another clue and, that is, there's noise when the engine is not running. Immediately when the engine has stopped turning, there's a noise that winds down as the rpms drop on the spinning fan. I believe it's your modulator fan or what some call fan clutch assembly.

Do this:

Climb up over the fan and lay on the shroud. Remove tension off the belt. With both hands, grab each side of the blades across from one another. Now, attempt to rock the assembly perpendicular to the shaft. There should not be any movement. IF it rocks side to side, it's shot.

It's also not supposed to free-wheel for seconds like that either. THere's some resistance in it spinning normally and, in your case, it's extremely easy to spin and, it continues to spin for seconds after the engine was cut. Nothing else was moving and, all engine parts including the water pump had stopped rotating but, the noise continued on for a brief moment followed by a drop in both volume and frequency as the fan went around and slowed down over time.

But, all say it's fine so, who knows.

EDIT: correction: I had to closely watch it again and, indeed, I was incorrect in stating that the motor was not rotating when it was. That means that the water pump and ALT, timing chain, power steering pump etc, were all rotating.

To check if it's your water pump, remove tension from the belt and rock the fan assembly as was described above. Any movement and it's shot.

 

Sorry to say.....but to me....It sounds like a broken piston ring at the front of the engine...cyl.#1 or 2. You also said there's oil missing?..(oil ring??),...that hollow tapping/clanging sound goes along/in tempo when you accelerate,..giving me this impression. (Check out the other clanking/"rubbing" senarios,...hope it's not my analysis. GL. **(my first guess,..that I shoved aside, because you said the noise wasn't coming from under the valve cover, was a very "loose" rocker arm/rocker arm off its mount/push rod...clanging away). **3rd and final guess: broken metal head gasket,..part of gasket shifted, and is hanging inside/being "hit" by the piston on its "up" stroke,..so many guesses/variables when you're not with the truck in question,...even though the video is good. ***Try what CMCKenna said first,...if that's it...hope so 4-your sake.

 

With a broken pistion ring wouldnt the truck be burning oil at a pretty fast rate? Causing lots of oil smoke out of the exhaust? If he's doesnt have that. I think we can rule that out. With a broken head gasket he would be missing coolant right? And it would be in his oil also. Either that or it would be weeping out of the engine and he'd smell it right? I dont think its anything that exteme at all, i beleive it to be up there in the pully system somwhere. I think he should still look/listen too that tensioner very closly next time he's out. But i may be wrong still...

 

Agreed, no weeping, no smells, not burning, no smoke, engine (less the sound) runs and rev's smoothly. Every head I've blown has had caramel frappee oil, white smoke, candy shoppee smell.

 

Just pumped that clip through my audio recording monitors and cranked it up a bit more. Well, above and beyond the higher pitched clacking, there's a deeper, hollow sound and, there's a resonant frequency that sounds like combustion on an open port.

Someone had mentioned exhaust manifold leak and, that may be what this is. You may have a cracked manifold or, a partial gasket blowout at the manifold. Check for leaks at the manifold.