Hum may also include other harmonics of 60 Hz. (120 Hz, 180 Hz, 240 Hz, etc.) Sources of the problem: Some solutions: 60 cycle AC and its harmonics - secure connections to ground. - use shielded, ...

It’s not uncommon for there to be a 50 or 60 hertz hum in audio equipment thanks to the effects of ground loops. Now that you’re an expert, solving the problem (or avoiding it entirely), is ...