i am typing on an ergo white modded board right now and i can indeed confirm that there is approximately 1 in 30 switches that has a slightly different click sound. i have experienced this with both pcb and plate mounted boards it is definitely a switch issue.
the most accurate i could describe it would be, that they are different in terms of hollowness/reverb of the click, some just sound dryer than others. there are fluctuations towards both extremes, so some might get near blue sharpness and some might have their click on a very low sound level instead.
i'll have to test if my microphone is actually capable of recording this properly, if so i could post a video later should someone be interested.