No clue. But it's Potter, so, probably? :shrug:
If you consider this the more grown-up version of Flight of the Hippogriff, then you don't really need on-board sound. On that ride Hagrid talks to you at load and during the lift hill as you bow to the Hippogriff, and then it's fast fun coaster time. No sound needed other than your own screams of glee. Maybe this will be similar to that?
The scenes on this ride that require sound (Flying car driving, Hagrid in the hut, fluffy barking, whatever's at the spike, devil's snare, etc) all happen during slow downs, and for the most part, inside of structures of some sort. They all make sense with proximity sound too, like sound seemingly coming from a specific source.
If there was sound on-board, I would guess it would be for music, which is an important element of the Potter films, so I can see it being used. But, I would not say it is necessary on a fast coaster. So, I can see pros and cons to including it on the ride.
In other words, :shrug: