Obviously newer models are different from older models, and Air models probably don't have the fans that Pro models do, but the claim that Macbooks don't have fans is a bit too broad to be true.
This is why these 'simple' naming schemes are confusing.
In Jobs' 2x2 matrix, the portable half was initially populated by iBook and PowerBook, later by MacBook and MacBook Pro.
It's unfortunate that Apple has confusing brand names, but the fact remains that the Macbook indeed has no fans so the original comment who hears fan noise is obviously using a different model of laptop.
So if you say that recent Macbooks have no fans, that may well be true. But it's not true for all Macbooks.