I've used these to replace some intake fans on my server rack, now I have pleasant sound of a wiresaw coming from it as opposed to the previous jet engine explosions.
I'm happy with my purchase, if you are using this for a home pc= don't bother, use some other noctua fans which are designed for a home pc. These are robust, loud and can melt your fan headers if your motherboard has low quality 6w pin headers instead of the more common, decent 9w ones.