Engine sounds are the noises that come from an engine, usually a car or truck. The term 'PURRS' is used to describe the low, steady sound of a well-running engine. 'ROARS' is used to describe the loud, powerful sound of an engine revving up. 'HUMS' is used to describe the low, continuous sound of an engine running at a constant speed. 'Pings' is used to describe the metallic sound of an engine misfiring. Finally, 'vrooms' is used to describe the sound of an engine accelerating quickly.