I’ve got a stumper for you:
97 Corolla 1.6L. The A/C belt goes around three pulleys: crank shaft, idler, and A/C clutch. When I remove the A/C belt the squeak goes away so I assume the problem is with the idler pulley bearing or A/C clutch bearing. I’ve replaced both bearings but it still squeaks. Why?!
Facts:
--squeak gets faster as engine RPMs increase
--squeak is constant whether A/C is on or off
--the A/C worked over the summer, but I can’t tell if it still does (it’s below freezing outside)
--I’m confident in my ability to tell the difference between belt squeak and bearing squeak
I was also confident in my ability to tell the difference between belt squeak and bearing squeak. A few weeks ago, I thought my water pump was on its way out until I replaced the serpentine belt. The squeak disappeared.
Have you tried a new belt?
No, the belt (Delco brand) only has 17,000 miles on it so I didn’t want to replace it. Additionally, no matter how tight or loose the belt is, the squeak sounds the same.
It wouldn’t make sense for the squeak to be from the belt, but then again, I’ve tried everything that does make sense.
Replace the belt. It may only have 17K on it but they do dry rot sitting on the shelf.
Replace the belt, I had a belt squeaking and it did not clear up until I switched brands of belt. Make sure all the surfaces are clean, no oil or belt dressing on them
Alright, alright 
I’ll replace the belt. I’ll try one from the dealer sometime this week.
Thanks to everyone who replied! I bought a new OEM belt from the dealer ($31.83!!) and so far, I’ve been squeak-free. I’ve found that, even though OEM is sometimes twice as expensive as generic, it’s cheaper in the long run to go with OEM.