AN excellent program called SoundSoap for the Mac can do wonders cleaning out that fuzz.

One cause of hiss is th einternal noise on the Mac, but it can often be filtered out just by recording at lower gain. Additionally, in AUdacity, you can impose a ten-section Equalizer (EQ) which enables you to increase or decrease the levels at various frequencies. By experimentation you can find the frequency band of the hiss and minimize it. Another source of his is using the wrong mic or mic cable--if it is high impedance it can cause a hiss. The high-impedance cable uses only two of the three available wires in the cable. As a result the sound may be imbalanced, causing the hissing sound. A decent condenser mike with a low-impedance cable (using all three conductors in the cable) will make it much cleaner.

I do not know if this is aproblem when using the internal mic (I mean unbalanced sound) but you could try dropping the input gain in AUdacity and then try perking it up afterw recording. Hope this helps.