If anyone has any ideas about this please let me know. I have a 1988 4Runner with a 22RE and an automatic transmission. Not every time, but often, when I am going up a hill at highway speeds, I get a high pitched squeal (kinda like a belt, but more metallic sounding) coming from what sounds like the passenger side of the engine bay, possibly near the starter?
I have no clue what is causing it. I have checked all the belts and it doesn't do it when the truck is traveling on level ground, only when the truck is in a bind like accelerating going up a hill. As soon as I let off it is gone, definitely correlates with the engine RPM and not the vehicle speed.

Anyone have any ideas?

 

Check your drive shaft U-joints.