[madoni]

I imagine you could filter out the 48-52Hz range (probably less) and make your fake recording unverifiable.

Taking the audio from the time you want to claim the recording took place and adding it shouldn't be too difficult either, though that might leave other clues that it's not genuine.

[haldean]

Except you would get the harmonics at 120Hz, 180Hz, 240Hz, 300Hz, etc.; there are some harmonics that are going to be within voice frequency that you wouldn't be able to filter out easily without taking out some of the body of the voice. It would (at the least) be obvious that the signal had been tampered with if it were missing all of the 60Hz harmonics.

[sneak]

In the US, the hum lives at 60Hz. And of course as others have pointed out, there are harmonics.

[dkokelley]

Another approach, dub the inverse wave of the real hum over your recording, which should (in my limited understanding) cancel the hum out, leaving a humless recording for a fraudulent hum to be overlayed.

[levlandau]

Right. I am more interested in the scenario where you fake something that is judged a genuine recording but is actually not.