Rich, read my Big Typhoon and Zalman cooler reviews. You'll find something interesting about how companies rate their noise levels!
The Big Typhoon puts out "16db" and is louder than the Zalman graphics sink in "silent mode" at something like 21db. Oh yeh, someone's not measuring their SPL by standard conventions there...and it's probably the one with the more outragiously low numbers, Thermaltake.
And this applies across the board, many companies publish numbers that look more like conservative estimates than reality once you hear the things. What's worse, review sites, lacking the proper testing equipment and sound chamber to get an accurate reading, simply publish the advertised numbers.
Oh, BTW, I just give estimates. My estimates are based on comparison. And estimates based on comparison, as aweful as that sounds, are more accurate than published numbers based on non-standard conditions.