Guitar strings and pickups act as excellent antennas for interference to electronic devices. Often something within your house iteself can cause the interference you hear through your amp. Aquarium heaters, electric blankets, curling irons, LED lighting, there are any number of sources. One way to track it down is to listen for the hum/buzz and, one-by-one, have someone shut off circuit breakers within your house. If the hum/buzz goes away when one of the breakers is shut off then your interference sourse is on that circuit.

I am involved in the radiocommunication field and this is how we track down localized interference. It's worth a try.

Old Cat.