On some bad mobile browsers combined with old devices, I think you would have to stop every sound using the "Stop Sound action" and verify a variable "muted" to play them or not.
As for master volume and such, I think even chrome on android has issues with it, I wonder if I should try to wrap up some tests to report bugs to the chrome team.
Hey — Please do, I'm having the same problem with the "set silent" function and the "master volume" function on my Android 4.3. Thanks. It would be would appreciated.