Because they're enjoying the concert. (kaching!)
Oh, you mean the computer's fans? You must be very proud of it. (ba-boom kaching!) Thanks! I'll be here all week. Try the veal!
Fans inside computers are there to cool them down. Computer generate heat as a waste-product, like a car engine, and that heat can also damage the electronics inside. The fans draw air into the case to force the heat outside. If you put your hand behind your computer, you should feel a warm breeze coming out the back. If you felt no air coming out of the computer, maybe one of your fans has stopped spinngin altogether, especially if part of the case is super hot to the touch. So a little warm exhaust is to be expected. Imaging a politician opening his/her mouth. That about the amount of hot air you should expect out of your computer.
Now, the fans in recent Macs are temperature sensitive. There are temperature sensors (called thermistors) on the heat generating parts of the Mac, like the processor and the hard drive, and sometimes others as well. As it gets hotter inside the computer, the computer speeds up the fans to cool itself down. And as the fans spin faster, they make more noise. So if the fans in your Mac are running high, it's either because it's getting too hot inside your computer or the thermistors have failed/can't tell how hot it is inside. How can you tell?
When the fans have gotten loud(er), quit every application (like Word, Mail, Safari) except for the Finder and wait about 1 minute. If the fan noise starts to go down, the CPU was busy, generating too much heat, and the fans had to rev up to cool the machine down. This can happen with applications that max out the CPU to 100% - or in English, programs that take up as much of the computer's processing power as they can get. Apple has a Utility called Activity Monitor than can show you in real time how much CPU each program is using. If you have a program that pegs the CPU to 100% or close to, then expect the fans to rev up a bit when you run that program. That's what they're for. After you quit that app the fans should gradually quiet down.
If you don't like fan noise (say you have tinnitus from teaching Karate for 40+ years) then there's a way to quiet the fans down a bit. Go into System Preferences under the Apple menu and click on Energy Saver. Click the Options tab, and you may see at the bottom of the window Processor Performace, and it's probably set to Automatic. Try setting it to Reduced – your mac run slower but quieter. If all you do on your Mac is email and web surfing, you may not notice any difference other than quieter fans. You can always change the setting back to Automatic or Highest at any time; it takes effect immediately.
If the fans are running loud all the time (from the time you turn on the Mac until you turn it off) or the fans get progressively louder all the time no matter what programs you run, then you might have a hardware problem. Call AppleCare or your local Apple dealership, describe your Mac's symptoms, and ask for help. Macs are usually fairly quiet and only get louder when the processor gets busy. If your Mac suddenly sounds like it's about to taxi down the runway and take off... yeah, you might want to have that looked into. Your Mac should only sound like the roar of a rock concert audience when it's doing something to deserve the applause.
Send in your questions! Email them to
