PSU fan louder than before?

[mace200200]

So lately I've been hearing a new noise in my computer which I could only assume was coming from a fan, I think I've narrowed it down to my PSU's fan. I've had this PSU for maybe a month or two, I don't care that it's loud, it's actually still not as loud as some of my case fans the only reason that it sticks out is because it's a much lower sound than my high pitched rosewill fans. My PSU still runs very very cold, and the air coming out from behind it is very very cold, and the fan still seems to still be running as fast as before, but I just want to make sure this isn't something that I need to replace, or worry about.

PSU (mine's 750w, but i can't find it): http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=125449&CatId=5431

 

[mace200200]

....so I guess the fan is just running louder because it's worn in now after a month and there's nothing else for me to worry about?

 

[Engima]

Are you sure that it is the fan making that low pitch humming? I didn't think fans of that size could make a humming noise...