Loud noise coming from fan

I was just taking apart my desktop and cleaning it up/blowing off the dust using a pressurized air gun (not too pressurized), and now that I have the nuts and screws back on, I plugged it in and the loudest noise began to come from the cooling fan.

It sounds as if theres something hitting the fan as it turns, this only happens on start-up for about 5 seconds as the fan blows at full speed. I did a visual inspection and there was nothing close to the fan, all wires were tucked away. What should I do?

It's possible that when you blew compressed air through the cooling fan, some grit/debris inadvertently got into the fan motor pinion. It should eventually work itself out, but if it's stubborn then try blowing more compressed air. You might also want to check if there's a lubrication port somewhere on it (some of these fans are completely maintenance free, but some can be lubricated).

Good idea, never thought about debris getting in there. i'll clean it up again tomorrow.

It doesn't look as if theres anything in the way.. I accidently put my hand in the fan and broke off two of the blades (lol). Now the noise is on and off. Is breaking the rest of the blades an option for stopping the noise? You know, like those new Dyson fans.

I've heard of the "blank" hitting the fan but never a hand. :D

I don't think that breaking off fan blades is a good idea. It might solve the noise problem but, now it would be useless for cooling.

The noise only is at start-up when the fan is going at full speed, after that it slows down and spins at regular speed. Honestly if this noise continues I will end up with "blank" hitting the fan, the wall, and the customers.

The computer doesn't need to be cooled down, the most action its ever gotten was when I had two word documents open at once with google chrome in the background.

I would just get a replacement fan. It's not a good idea to run a computer without a properly working fan. You just never know when temperature tolerances might be breached and ruin hardware. Fans are cheap. CPU's and motherboards are not!