Where could this screaming whining noise be coming from under the hood of my truck?

Show it to someone who knows about cars. They'll better be able to tell. There are lots of suspects in this crime and each one needs an interview. A wild guess is a loose belt, but other things could be dragging the belt. Could be a failed bearing or broken harmonic damper. No way can any of us check those for you.

In a previous question you mentioned it had been doing this for two months. It's time to take it to a mechanic.

I could be some woman.

I'm not sure but it was the hooker that didn't pay me my money so I threw her under the hood of my Porsche since the engine is in the back. Heard her screaming and whining for miles until she agreed to pay me my money.

Spray soapy water on the belt while the engine is running. Noise goes away, replace the belt. Noise does not go away, check the pulleys.

https://www.youtube.com/watch?v=AEUe6uKxTv8

If it's a high-pitched noise that changes pitch with the engine speed and is coming from the alternator, it could be a shorted diode or a shorted stator winding in the alternator.

If it's a screechy metallic noise coming from the alternator that doesn't seem to change pitch with the engine speed, it could be the front alternator bearing or the rear alternator bearing.

If it's a rubber squealing noise (like squealing tires) it could be the belt squealing (from slipping).

It could be a belt idler pulley bearing or a belt tensioner pulley bearing.

See if your belt tensioner is stuck from tensioning the belt. Move the tensioner with a 3/8" ratchet or breaker bar with the engine off. Sometimes the belt tensioner pivot gets corroded and the tensioner can't move and the belt squeals at the alternator pulley, especially after just starting the engine.

-Engine overhaul mechanic and general automotive mechanic since 1972. Retired in 2018.

Use a long screwdriver and hold the tip of the screwdriver to the alternator and the handle to your ear. If the noise is louder the alternator bearings are going bad.

It could be the alternator. Get a cardboard tube and hold it to your ear and move the other end around the engine to see if you can determine with certainty where the sound is coming from. If one of the three phases in the alternator shorts out it can unbalance the alternator and cause a whining noise.

Also, you can switch your car radio to the AM band and tune to a blank spot. Turn up the volume and see if you can hear that noise in the radio. It may help to turn on the headlights and heater fan to load the alternator first. Of course, if you hear the whining noise in the radio then your alternator is bad.

My van developed a weak tensioner pulley spring .......

Have you checked all you’re fluids, especially power steering fluid?