For me it turned out to be an instant water heater trying to keep pipes hot. Went at the electrical stuff first l. But even after engaging local power company a

For me it turned out to be an instant water heater trying to keep pipes hot. Went at the electrical stuff first l. But even after engaging local power company and long distance distribution folks, nothing was done. But, turning off water heater at night stops it. So much relief after years of noise.