Some of it is cosmic background radiation - it’s also machine vibrations, manufacturer defects, power line radiation, and nearby appliances. The more remote and well shielded you are the more likely it’s pure background radiation… but in a big city it’s likely to be local radiation sources. The inverse square law has a big role here.
Snow or static. It’s cosmic microwave background radiation - the remnants of the big bang.
Some of it is cosmic background radiation - it’s also machine vibrations, manufacturer defects, power line radiation, and nearby appliances. The more remote and well shielded you are the more likely it’s pure background radiation… but in a big city it’s likely to be local radiation sources. The inverse square law has a big role here.