And now, if you want to do a 'little' improvement, you may use a PIC with a HPWM module and, if possible, use this module to generate the tone. This may avoid some unwanted 'distortion' in the tones. HPWM will continue to play the tone, while sending your info to the LCD. BUT as i'd didn't heard the actual result, i can't say if it's going to be a real improvement.