Sounds like his vocoder got plugged into an amp. It's an interesting concept, having a proto-Vader voice that is still finding its way. I think it would work pretty well if Vader had more than one scene. As it is, it'd seem weird to me to bring in JEJ for a few lines that wouldn't sound much like him. Plus, hearing JEJ's Vader asking about Padme gave me chills on opening day.

If the film had been otherwise, I'd have preferred a proto-Vader with a voice and look that showed a trajectory for the OT Vader, rather than to see Hayden dumped into a fully recognizable OT replica. (And I wonder whether his vocoder automatically enhances Anakin's annunciation. I don't picture the PT Anakin's voice underneath those line deliveries at all.)