Here's what I found through a quick Google search. I don't have my table handy and this system isn't touch enabled so I can't test though. Let us know if it works.
Steps To Turn Off Touch Keyboard Sound in Windows 8
Step 1: Take from the right side of the screen and open the charms menu. For those users who are using it on desktops can use their mouse to move to upper or lower right corner of the screen or use their keyboards to press Windows + C keys to see the Charms bar.
Step 2: Select settings and then click or tap (if using on the tablet) Change PC settings to open PC settings on your screen.
Step 3: Select GENERAL in the left – pane of the screen and there you will see lay key sounds as I type. Those users who are using windows 8 on non-touch devices cannot access this option.
Step 4: Move the slider to the left to turn the sound off, if you need to turn it on slide to right to enable sound.