WORRISOME ENGINE SOUNDS are noises that can indicate a problem with an engine. The two crossword solutions for this term are KNOCKS (6 letters) and PINGS (5 letters). KNOCKS are loud, rhythmic thuds that can be heard when an engine is running. PINGS are high-pitched sounds that can indicate a problem with the engine's fuel or ignition system. Both of these sounds can be indicative of a serious issue with an engine and should be addressed as soon as possible.