Atmospheric And Solar Generated Noise

Plus some internally generated receiver noise

These types of noise interference are not only very common but quite natural in nature. The sun creates a lot of the noise we hear on our radios but so does planet Earth and other celestial bodies in the sky. Solar flares on the surface of the sun are a major source of noise. Magnetic storms can wreak havoc on radio communications.

Similar noise is generated in the front end and every subsequent section of the receiver. A certain amount of the constant background hiss you here coming out of the speaker is generated within the receiver itself. To demonstrate this, disconnect the antenna and see how noise is still there. Even the DC power supply hsh some level of hash but much of these noise get filtered out before reacing the audio stages, which themselves generate some some amount of noise.