What?

We're writing a script for a new documentary about hearing loss:

Act 1, Scene 3, the family car.

Jamie: [something incoherent]
Dad: Walking?
Jamie: No, [something incoherent]
Dad: Rockin' and Rollin'?
Jamie: No, [something incoherent]
Dad: Ooooh, a rocket?
Jamie: NOOOO, [something incoherent]
Dad: I just can't hear you. Can you say it louder?
Jamie: ummm... [now, correcting himself] UMMMM... ummmm... [something incoherent]