Motor sound is a term used to describe the sound made by an engine or motor. The crossword solutions for this term are PING (4 letters), HUM (3 letters), PURR (4 letters), WHIR (4 letters), and DRONE (5 letters). PING is a sharp, high-pitched sound, usually made by a metal object striking something else. HUM is a low, continuous sound, often made by an engine or motor. PURR is a low, continuous sound, similar to a PURR made by a cat. WHIR is a continuous, high-pitched sound, usually made by a machine or motor. DRONE is a continuous, low-pitched sound, often made by an engine or motor.