Why do power lines hum?
Power lines don't hum, but the transformers that run them do.
The humming is a result of the interchange in the coils that
converts the voltage to a different level.
With "Smart Grid" technology, power companies are using the power grid to send/receive RF signals. These high or low frequencies co-exist with the usual 60hz being transmitted across the nation. Eventually, with the installation of 'smart meters', they can read power consumption without coming out to the site, eliminating thousands of jobs, and some suggest even turn your power on/off from a remote station. This technology also allows them to locate outages faster and identify…
EHV and VHV substations tend to have a signature hum; this is due to small electrical arcs. This is normal. Most of the time this will not be audible on VHV and EHV power lines. If you are hearing this from the power line, it could be bad and the utility may want to know. It shouldn't be a risk to you, however the hum may be resulting from arcing, which can be fairly high…
Power lines and phone lines though using the same utility poles are two different sets of wires. Telephone wires carry their own power, separate from the power lines and are insulted while power lines are not. If the telephone wires are unbroken but laying on the ground the wires will not short to ground while an unbroken uninsulated power line will short to ground disrupting service.
Sagging Power Lines In the summer, power lines warm up with the weather. Since materials expand when they get warm, the power lines stretch out and sag. The opposite happens in the winter, as the power lines get colder, they contract. Also, in the summer the electrical load on the line is generally greater. This in turn causes increased temperature and can lead to the line sagging.
Mixers are complex pieces of equipment and mains hum can be induced from a variety of sources. In many cases, it is due to earth loops or other earth issues. In some cases, a power supply may give rise to noise on the outputs. Ferrite cores clipped to a cable are unlikely to make any difference to the hum. Get the connections right and the hum will probably disappear.