I have a Dell Powerconnect 2824 24 port Gigabit managed switch in the attic above my bedroom. The switch introduced easily audible noise into my bedroom system, even my wife complained about it!
So I ripped out the screaming Delta fan, cut away the fan grill stamped in the case and installed a lovely little Noctua fan. Result: no more noise! Total cost: £12.72 and 30 minutes of my time.
Offensive screaming Delta fan...
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Note: The 16 port version of this switch is fanless and goes for £50+ on eBay. I paid £38 for the 24 port version with it's noisy fan.