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If fans are always turned on, the first thing you should try is to reset the SMC > http://support.apple.com/kb/HT3964 This will reset fans speed to default settings, so if it's a software problem, it will be solved.
If it doesn't work, take the computer to an Apple Store to get it repaired
Depends what you mean by a lot of noise. Do they sound like they're running very fast or are the fan motors making grinding or screeching sounds?
You can check to see what the fan speeds are using iStat Pro widget.
The suggestion to reset the SMC is a good one, just in case the power management in your Mac needs a reset.
However, the fan loudness depends a lot on the type of Mac you are using, and also on the programs you are running.
Our iMac (2008) Core 2 Duo has fans, but you'd never know it as they run only with the quietest hum, if at all, or I just can't hear them.
On the other hand, the last two Macbook Pros that I have had (2010 and 2012 models) were usually quiet but their fans would revv up quite loudly when viewing streaming video, doing certain things in Firefox, etc. My daughter's Macbook Air is very quite except when running PhotoShop + iPhoto + Firefox and then its fans get loud.
You have a Macbook pro. Do the fans run loud always, or only when you use certain programs, video, etc.