Audacity has decent noise removal (Score 1)

Audacity has a noise removal effect that was able to remove a really horrible hiss after a hybrid decided to stop behaving before an interview (shameless plug for University Radio Hilo). It takes a sample segment that should be the noise by itself and can then be applied to the rest of the file. It won't improve the source quality, but it might help with the hiss, especially if it's really constant.