A teenage boy says what?

I've noticed a trend with my son. It really started about a 1 1/2 years ago. We ask a question and get the answer of "hum, mmm, mmm, no." When we tell him that we did not understand what he said, the same nonsense comes out of his mouth. I guess they are words. He says they are words. He even gets upset that we just don't listen to him. Apparently I don't speak teenager. Does anyone? It will be an interesting few years :)