My main desktop PC used to sound like a jumbo jet taking off. I've just fitted two 'quiet' 120mm chassis fans and a quiet CPU fan, along with a filter (pack of ten). The whole lot cost me just over twenty quid (about 25 USD). My God, the difference! I can barely tell it's on now. I would highly recommend 'quiet' specification fans, though I suppose most people use laptops nowadays.
These days there are so many different models of quiet fans to choose from its hard to decide, but it helps to have a case that's actually designed to be quiet in the first place if its really important to you. This website has reviews for anyone interested: http://www.silentpcreview.com/
my laptop can get annoying sometimes, but its usually just during some update. funny last night I heard it, so I turned on the room fan to muffle it.
when mine starts working overtime i blow it out with compressed air and then it gets nice and quiet again
ive been vacuuming my keyboard on the laptop .. ever since I took the last one apart, with all those ashes and dust in there. yucky..
Laptops have shit cooling and a quiet laptop is a 'days numbered' laptop. Happiness to me is having none of my chips, especially GPU's, running over 60C degrees.