Reduce background noise from a .wav file?
Noise usually creeps up at various specific frequencies in audio, these frequencies change depending on the environment.

Option 1
The easiest way to get rid of noise is the put a band pass filter right around where the frequency of your voice is at. There may still be noise at the same frequency of your voice, but this will be much harder to deal with.

Option 2
I am not sure what Audacity does, but I have seen many programs that require a sample of "silence" and use that to determine the noise. In other words, you record your voice but leave a gap of dead air at the end or beginning. Then you can go analyze what frequency components are around in your dead air. From this you can know how much of each frequency to remove from your voice signal.