Sone is a measure of perceived loudness, I've come across it before in measurements of acceptable sound levels for the work place. According to wikipedia the unit has been around since the 1930's, not too obscure.
Anyway according to the wikipedia table
here, 6 sone would be equivalent to an SPL measurement in the region of 60 to 80 dB. Which is rubbish for a cooler. I think that must be a mistake since lots of reviews have said the Accelero with a fan is fairly quiet. I'm quite interested to see this product reviewed.