It has an aftermarket radio but that has been installed for about 2 years.
OK, so you've had no "whine" noise until recently... "new", as you said.
I could tell you how to check the alternator with an oscilloscope, but I'm guessing you don't have access to one.
Personally here's what I would try:
Disconnect the alternator plug (probably looks like this below) and see if the whine goes away. If so, it means the whine's somehow related to the alternator... at which point I would probably swap the alternator with another to see if the whine disappeared.
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Meanwhile,
@jd33173 gave you some good suggestions for alternator and/or belt-related noises. The noise you're hearing MAY be something other than these, of course.
I’ve changed the fuel pump, and I switched the taillights, third brake light, and turn signals back to oem halogen from LED. Not sure if any of these could possibly be related.
I wouldn't
expect these to cause a whine. However...
When you changed the fuel pump did you confirm the condition of its ground wire? I have a Suburban, and my pump grounds to the frame in the rear. On the pickups, I assume the pump grounds on the frame as well but I'm not certain of the location.
I'm not saying this is related to the whine, I'm saying it's worth checking