Recently, my dad's 2016 explorer sport had a kind of clunking feeling coming from somewhere in the drivetrain, but only at low speeds, and usually only in reverse. At low speeds (less than 5 mph), the transmission would clunk, and the car would shutter. About a week later, we got six inches of snow here in colorado, so I drove it to school. When I put the car into snow mode, I could hear a low basey sound coming from the transmission, and experienced the shuttering and clunking while reversing into a parking spot. I thought it was just traction control, due to the massive potholes in the dirt parking lot. Yesterday, my dad brought the car into the dealer to have them look at it. They said it was a PTU failure, and will be replacing it under warranty. It's surprising considering it only has 35k miles. Anyone else having this problem?