At the dealership now. I test drove another Gladiator and it was exhibiting the same issue. Looks like I'm going to have to live with this one for the time being.
The gauge cluster uses an LCD display, and LCDs are prone to whine at full brightness. I agree it's super annoying. I'm going to ask my service advisor if anything can be done. Maybe they can set the auto-brightness to a tad less than full??
I noticed this as well. It's super annoying when I'm trying to cool off and the heat is blasting set to 65 degrees. Leaving it on auto solves this problem for me, but there needs to be a better workaround.