I would say idler or tensioner pulley, maybe.
Hmmm, sorry this is bothering you.Just figure out where the noise is from or go see a mechanic.
You've had enough feedback to put you in the right direction. It's not that complicated!
My apologies clyder,Hmmm, sorry this is bothering you.
No biggie.My apologies clyder,
I see now that you're actually really chasing down a hard to find noise, I didn't mean to offend.
The "hose to the ear" always helps me to quickly find the source, but I see now you got a stethoscope.
You could always remove the belt to be sure it's an accessory making the noise.
With the belt off you can check accessory bearings for problems.
I have had the chirp also. Before my alternator quit charging I had a whine for about a year. After I replaced the alternator the whine was gone.The posts suggesting it may be the alternator or a pulley sound plausible. But I would think it's more of a "chirping" sound instead of a "whine"???
Now that you've narrowed it down a bit, two things I would do before condemning the pump:No biggie.
With the stethoscope I am fairly sure it is the pump making the noise. You can hear a slight change in the whine when moving the wheel with the scope.