Remove hum from sound file?

[furnace]

What's the best program to remove a hum from a sound file? It needs to be free. I have tried Audacity which seems OK using the "Noise Removal" effect, but it's not great...

Are there any other suggestions, or any tips & tricks, for doing this?

 

[furnace]

Unfortunately not

I've got the CD's that need fixing now and I thought it'd be a low hum but it's actually a high pitch hum, maybe from a laptop hard drive or fan. Audacity seems to get rid of it well enough, albeit with somel loss

Thanks