HISS (5 letters) Radio static is a type of noise that can be heard on an analog radio signal. It is usually caused by interference from other signals, such as electrical equipment or atmospheric conditions. The two crossword solutions for the term 'radio static' are 'CRACKLE' and 'HISS'. CRACKLE is a sharp, crackling sound that is often heard when tuning a radio, while HISS is a continuous, low-level sound that is often heard when listening to a weak radio signal.