Clicking sound is really annoying

I like the app very much as it replaces an HP11C calculator emulator I had been using. The sound however is really annoying and sounds more like a manual typewriter key than the true calculator button my HP11C and 15C physical calculators actually make. Please offer an option to turn off the sound. And please replace the sound with the real thing. You emulated the calculator very well, how about the button click?

Jrojai about HP 15C Calculator