Viper Lair posted a review on the Zalman CNPS9500 AM2 Quiet CPU Cooler

The CMPS9500 AM2 was very quiet throughout testing. It spun up to it's maximum speed once it hit full load, but it took over 3 minutes to do that. Basically, if you tend to load up your CPU in short bursts, the cooler may never hit full speed. To be honest, I'm not really sure of any real-world examples of that, but in day-to-day use, it will not be very disturbing.

Zalman CNPS9500 AM2 Quiet CPU Cooler Review