I wonder if what you're experiencing is something called "ripple control" (in Australia).
Distribution companies send 10-40V signals through the system at much higher frequencies than the normal 50/60Hz of AC systems (750-1100Hz) to tell old controlled load devices to switch on or off to use cheap nighttime power.
Having said that, if your distribution company has no idea what it is then it makes this less likely.
Distribution companies send 10-40V signals through the system at much higher frequencies than the normal 50/60Hz of AC systems (750-1100Hz) to tell old controlled load devices to switch on or off to use cheap nighttime power.
Having said that, if your distribution company has no idea what it is then it makes this less likely.