My brother just picked up a 2010 Tahoe LT 4x4 and it has been driving very well until today. He called and told me while he was hard into the gas passing someone that he heard an audible bang from under the truck and let off the gas. He passed another car a minute later and said it did not make the sound. I'm a competent mechanic and can take direction but I dont have much experience with Tahoes. What could have made the noise? My first thought is the trans disengaging and reengaging under throttle. What can be done to fix it? Thank you all ahead of time.