Just built this circuit out of curiosity about the expected sound not knowing what a laser ray sounded like. I thought it would be a 'hum', like when James bond was strapped onto Goldfinger's laser table. What I managed to produce was a loud rapid clicking to sync. with the flashing LED. Is this right? Anyway with a few changes to the 220k resistor I ended up with a sound not dissimilar to the old geiger counter
used for detecting radiation. In fact it is exactly the same sound as I recall. To achieve this sound change the 220k resistor for a 470K resistor.