If your Wii is making noise, first insure that the surface it is sitting on is solid. I do know while on it's side it is more prone to vibration noise, sitting it flat without the stand will help that annoyance.
Also, examine the discs. It has been reported that the "loud" Wii's have been munching the outer edge of them, and if it is doing that it is time for repair.
If the Wii is freezing or giving you "Cannot Read Disc" errors on multiple games, it is time for it to be sent in. Even once a week is too frequent. It seems most people have gotten this at least once, either due to inserting the disc in upside down or because they take poor care of there game discs. Continued use of the cardboard sleeve for Wii Sports will also result is a scratched disc. If the disc is clean and you are still getting errors, it is time for repair.
Those who are saying "it works great", well it's not supposed to be that loud and probably a matter of time before failure. Keep that in mind. It seems that Nintendo had shipped a bunch of Wii's with bad drive motors which got past QC, and is the source of this problem.