I drive a 2013 GMC truck. I get a whine from under the dash when I apply the brakes.
I have been advised it is the power brake booster. Any real mechanics here that can shed some light on this issue?
I do have a recurring check engine light that comes on goes on its own.
Truck stops fine as always.
I have not been able to hit the emissions station as the check engine light is an automatic DQ.

Pretty sure O'Reilly's auto parts will plug into the ECU for free and read the codes to give you an idea of what's going on with the check engine light

Dunno if braking systems are similar from my 98 3500HD to yours, but my hydroboost went south a few years ago. Truck still stopped fine, but was getting some pretty aggressive sounding groans from underhood. Good luck.

Bruce, can you share some more details about your truck? (1/2 or 3/4 ton, HD or not, gas or diesel, etc). The brake systems can be drastically different from a 4.8L single cab base model 2WD 1500 to a Dually HD 3500 1 Ton Duramax crew cab.

Brake booster failures are common and they will cause engine running issues. it is causing a vacuum leak.