Unfortunately, on the HSF, I would recommend just dealing with the sound, depending on your processor. They are usually loud because they do a load of work to get that CPU cool.
If you REALLY need to replace it because it's that bad, then you need to get a heatsink that rocks to make up for the less cooling power the fan will do. You'll also want to get a fan that is silent because of the constuction behind it, not because it runs at a lower RPM. Fans that run at a lower RPM are silent, but that's because they don't do nearly as much as a fan running at full speed.