The song or video to be precise (it was on YouTube) I'm searching for is from two young Americans (one heavier black male and a slim white male). It's quite old, pre 2010 if I'm not mistaken. As far as I can remember they both had a rap part and created the beat with beatboxing or hitting objects in the car. They were sitting in the front row and had a single camera placed on the dashboard.
I struggle to find it now because the Internet is loaded with 'car rap' videos and I don't remember any lyrics or names.
They went on to produce a full professional album and other stuff years after that video, so they should be findable.