Electronics

So I installed a shiny new mediocre panel heater from Namron (Namron WBL0636) for my tenants. It was cheap, looks ok and and heats the room. So what else could you ask for? Not much. After a while they started complaining about hearing some beeping sounds, and did not understand where they came from. I did not know neither, but after some time I understood that the heater must be the reason....