We went through a period where we removed the sound from the SD version of the rides to reduce the file size. All the new rides will include sound in both versions. If you really like hearing the ride you’ll need to download the HD version to guarantee hearing it.
It’s also worth mentioning that the sound only works properly when you ride in Steady mode. This mode plays the video at the speed it was filmed, whatever the effort you put it. In reactive and challenge modes, the video speed varies constantly. This results in very choppy sound.