Why is my processor fan so loud?

Why is my processor fan so loud?

My CPU stock fan started getting loud so I went and bought a replacement, this fan is still loud. what could the problem be? It is not unbearable loud, but i can still hear it very well.

Additional Details

I am not running games, just turn it on and it is a little loud. The thermal paste is on right, it is a brand new heatsink/fan so it isn't dirty. My video card is new too and is not dirty. I clean the PC regularly so it wouldn't be dust build up. Usually when I play games I expect to be able to hear it.

1 day ago|||Could be the other fan. There are two fans inside a pc. Forgot the name of it, but have that one checked out as well.|||Gets to hot...|||As the fan screws ontop of the heat sink make sure it is on there even ,spin the fan with your finger to check that its running free|||Most fans are pretty loud. its fine that it's loud because as long as its doing the job of keeping your processor cool.|||Do you over clock your comp ? Is your computer in a reasonable space to breathe ? As soon as your computer gains heat your fans will spin to cool it down BUT the more hotter it gets, the more the fans will spin, so your computer must be really hot. What about the power supply ? is it the right power going in to your computer ? perhaps this might cause it to heat much quicker