what's that awful clanging noise?

My boat is a 2001 Sea Ray BR190
My engine is a 5.0L EFI GM 305 V-8 1999-2001, 260 HP, model 4M31027N1, ser #OM068nnn

I've noticed an annoying clanging/rattling noise in the 1000-1300 RPM range. It goes away at faster or slower.
It is loud enough to make me wonder if something is being damaged. This happens even when the sterndrive is in neutral, so can I assume that the sterndrive is OK?

I first noticed this noise after I changed the serpentine belt last fall. Could I have installed the belt too tight or too loose?
If I buy or borrow a belt tension gauge, where can I look up the correct value?
What other troubleshooting techniques should I try?

I live more than 90 minutes from any marina. Is there any reason that a local auto mechanic couldn't diagnose this issue for me? Would he charge less than a marine mechanic?

Ayuh,.... The drive turns with the crankshaft, except for the prop shaft, so nope, it could be the drive,.....

I'd pull the drive, 'n try it,..... if ya still hear it,... Look closer to find it,....

Pull the drive? You mean the entire Alpha sterndrive?
I've never done that. How much does that thing weigh? Would all the oil have to be drained from it?
And, then, how would I connect water to run the engine with the drive removed?
That procedure might exceed my capabilities.

This "rattle" or "clanging" noise seems to have begun just after I changed the serpentine belt.
To me, that suggests that the sound is coming from the alternator, water pump, or power steering pump.
I'm just looking for a way to narrow it down to one thing.

I still think I might have over-tensioned or under-tensioned the belt.
Where can I find the correct procedure, including how to set the tension with a gauge?

This guy shows the procedure, but he guesses at the tension:
https://www.youtube.com/watch?v=63Q6m59QOuw&ab_channel=SternDrives

Ayuh,..... There's 8 nuts, 'n the drive is off,...... weighs 'bout 80 lbs,.... no need to drain it,....
You can feed water through the hole in the gimbel, by crammin' a hose into it,... I wire it in-place myself,....

If ya think it has to do with the belt,....... Take it off, 'n try it,.....