are you referring the the heatsink fan?
if so, i would suggest buying an aftermarket heatsink.
I have the coolermaster hyper 212 (costs about $30) on an i5 760 built earlier this year...that and an ssd to run the OS and my pc is very quiet
If it is the heatsink fan, it shouldn't be that noisy.
About a month ago I built an i3 2100 build with the stock heatsink and the thing is whisper quiet, so an aftermarket heatsink wouldn't necessarily correct the issue.
However, I do want to mention that I did have difficulty installing the stock heatsink as it took quite a bit of effort to ensure all the pins were secure. So please as Tamz_msc mentions, check to make sure it is installed correctly.
Unless you are mistaking the loud noise for a case fan or something else.
if you think about it, the cpu is one of the pricier parts in your build. It is worth it to pay a little to be sure it is cooled properly. Also don't under estimate the importance of a quality thermal paste.