The term RADIATOR SOUND is used to describe the sound made by a radiator when it is heating up. The crossword solutions for this term are SISS (4 letters), HISS (4 letters), SSS (3 letters), and SSSS (4 letters). SISS is a sound made by a hissing snake, HISS is a sound made by a snake or other animal, SSS is a sound made by a steam engine, and SSSS is a sound made by a radiator. All of these sounds are similar in that they are all high-pitched and have a hissing quality.