I'm sticking with my original diagnosis -- brake pads not disengaging. But the Whonp, whomp whomp still bothers me. If it's the brake pads, pull the wheels/tires, spray the rotors and calipers generously with Brake Clean - readily available at any auto parts store, Walmart, etc, don't worry, it dries very quickly and washes away a lot of crud. Then do a Youtube search for brake pad R&R for your model year truck (or close) just to educate yourself. Next, with the wheels and tires off (driver's side only if that's where the noise is coming from), identify the caliper sliders. Next get some WD40 or any sort of oil lubricant and put a couple of drops in and around where the sliders move. If that eliminate the groaning, then you've solved the issue and can go from there.
Others will have different suggestions, but in my simple mind, this is what I would do --- well not really -- I would wait until it broke, then I'd fix it. That's what my wife always yells at me for.