First of all, the usual warning: I take no responsibility for any harm done to yourself or your equipment if you decide to take my lead and mod the fan on your switch. It’s your fault for listening to some guy on the Internet you’ve never met.
A little while ago I acquired some old 3550 switches from a friend, and I haven’t used them much because they’re horrifically loud. Recently though, I decided to try and make them quiet enough to leave on in the living room. While I didn’t succeed, I made enough of a difference that I thought it might be worth sharing.
Please note that this mod isn’t going to work if your switch is a) under warranty; b) installed in an equipment rack with hot/cold aisles; or c) you don’t like taking the cover off equipment that has 240v inside.
Basically, the gist is this: The fan inside the switch has a cover on it. By removing half of the cover (the half that isn’t attached to the fan motor) and then mounting the fan upside down, you reduce the vibrations of the fan’s casing. Please also note that the outlet fan is thus turned into an intake fan; it takes cold air from the back of the router and blows it over the power supply unit.
Research on the Internet (#cisco on Freenode and some forums) led me to decide that complete removal of the fan wasn’t an option, due to the switch overheating. I then wanted to replace the fan with a quieter computer fan, but the connector, though the same, is wired differently. Though I own (and can operate) a soldering iron, I’m also quite lazy. Turning the fan upside down (as suggested by a friend) was much easier!
Update 2011-08-17: I initially tried this with my non-PoE switch. Today I tried this with my PoE switch and tested it running a few PoE devices. It quickly overheated, so I don’t recommend this with the PoE (inline power) models.