Double check the belt routing

 

Changing belt size to accommodate his faulty set up is not the answer.

There is obviously something wrong with the set up. I am going to assume that this problem has not always been there and that there were no pulleys changed prior to the problems arrival.

If these assumptions are correct then there is a loose pulley, a lazy tensioner, or incorrect belt routing.

 

I've watched it over about a dozen times. The sound doesn't seem to sync with the belt, that may be a separate issue (I'd guess tensioner).
The sounds sure seems to sync with the fan spin though and the fan looks like it's the kind with the enclosed ring around it, I didn't think Disco's came with those. I've seen them on the 4.6 Rangie's though.
Is that a stock fan?

 

i totally agree that it didn't sound like the issue was coming from the belt. That said, with the belt off the sound went away entirely. With the slightly newer (tighter) belt it's mostly resolved. So I think it is mainly a belt issue, even though there was clearly some fan interference at some point (non-stock fan, you're right)

mainly just trying to figure out now how to tension that sucker up

 

Unless I'm totally missing something with the belt off the fan wouldn't spin would it? Hence the sound stopping
My memory on that should be good as I just finished up a head gasket job.
And if that's a non-stock fan which it seems you have confirmed that'd be where I would be focusing.
Remove the whole shroud and run just for testing.

 

I'm guessing tensioner. Unless his is a non-ACE car and you're putting an ACE belt on there.