The term 'fizzling sound' can be described by two crossword solutions: PFFT (4 letters) and SSS (3 letters). PFFT is an onomatopoeia that is used to describe a sudden, sharp sound, such as the sound of a balloon popping. SSS is another onomatopoeia that is used to describe a hissing sound, such as the sound of a snake. Together, these two words can be used to describe a fizzling sound, which is a combination of a popping and hissing sound.