Dennis77

I have a 2014 GMC Sierra. Its recently started making a humming noise when I accelerate. It goes away the second you take your foot off the gas. It's been in 4x4 auto since I've driven it. I discovered that if you switch it to 2 wheel drive, the humming doesnt occur during acceleration. If you switch it back to 4wheel auto, the humming comes back. The differential? What is causing this and why?