5 Simple Steps to a Quieter PC
 

Silencing a computer can be a costly endeavor, but taking a few relatively inexpensive steps can have a drastic impact on the noise produced by the common computer system. Before starting on any sound reduction upgrades, analyzing a system to pinpoint the areas in need of the most attention will help determine the best course of action and the best way to spend any money.

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Sleeve bearing fan normaly is good for about 25,000-30,000 hours (more than 2 years 10 months) versus ball bearing 30,000 to 45,000 hours.

Frankly if you don't do a clean up twice a year, your computer is full of dust anyway and it really doesn't matter ball or sleeve bearing. When the cleaning time arrives, I normally re-oil the sleeve or ball bearing - a tiny drop of good machine oil.

Never have a fan bearing failure since 1979, ball or sleeve
bearings.

Added:
I started using teflon gun oil in the last 15 years.