if its making noise there are 2 options.
1 take the fan out, clean it and lube it up. To do this you need to peel back the sticker from the middle of the fan and remove a rubber grommit. you put a small amount of sewing machine oil in there or similar.
replace the grommit and should be good as new.
Word of warning, not all fans have this grommit, some fans are made to not be serviceable, they just get thrown away when they get old.
Now if you cant be stuffed doing that, get a new one.
For the sake of $50, you can purchase a brand new one. Same brand and a bit of an upgrade to your 300w.
http://www.techbuy.com.au/p/56806/POWER ... TX-400.aspbasically you shouldnt need any higher wattage PSU if you dont intend on putting more gear in your PC. but for $50 whos complaning?