Hum filtering can be doine VERY effectively by the noise removal algorithm that also gets rid of tape hiss, used by several programs. I recommend Audacity because it's totally free and works well for this type of job. It wll do recording, editing and noise removal and a number of other jobs, and it's multi platform - Windows, Linux or Macintosh.

The way the noise removal works is : you find a short section that has the background noise only, the progam samples the spectrum of that, then "subtracts" it from the rest of the track.

Anahata