I have sapphire 4890 and i get strange noise ( other than blowing, like "Prrr Prrr Prrr Prrr" ) i tried to change fan speed manually, i don't here that sound under %25 speed.
I've recorded the noise: http://www.mediafire.com/?sharekey=004f7a704f5c85c708f8df73f2072ed6e04e75f6e8ebb871
I've recorded the noise: http://www.mediafire.com/?sharekey=004f7a704f5c85c708f8df73f2072ed6e04e75f6e8ebb871