05RedZ71Sub

The other morning my wife started our 2013 Suburban and after a few minutes of idling she heard a pound bang from the front that startled her. She had turned off the AC just before and was syncing her Bluetooth at the time. She hadn't put the truck in gear yet. She didn't feel anything associated with the bang. Unsure what to do she drove the truck and had no other symptoms. We've used the truck all week and everything seems perfect. AC works, no error lights, idles fine. Looked under the hood and nothing wrong. No leaks anywhere.

I'm stumped. Thinking maybe something external to the truck made the noise but can't think of what it could have been. Any ideas?