I'm not sure if this is an SP3 problem, but changing the volume by the side buttons, muting and unmuting with the type cover 3, and the taskbar volume slider all seem to have no effect to change the volume, or play any sound at all. Usually, setting the volume would make a "ding" tone, which was not present, for example, the volume could be at 100%, but releasing the slider would not show a green bar that would also be present when the slider "dings". I then opened the playback menu, the tested the speakers - it would then say "Error: could not play test tone". I've already restarted the device once, it didn't seem to have any effect. I don't know if this is a Windows 8.1 problem or a Surface Pro 3 problem.