Whether button presses make a sound or not is controlled at the operating system level.
You can toggle this setting on or off (it seems to be on by default).
for Android 2.3:
go to Settings-> Sound settings -> Audible selection
for Android 4.2 and 4.3:
go to Settings -> My device -> Sound -> Touch sounds
for other versions of Android, there should be a similar option as well..
UChin Kim