The term 'SOUND OF A DUD' can be summarized by two crossword solutions: PFFT (4 letters) and PHFFFT (6 letters). PFFT is an onomatopoeia that is used to describe a sound made when something fails or does not work as expected. It is often used to describe a failed attempt at a joke or a failed attempt at something else. PHFFFT is a more emphatic version of PFFT, and is used to express greater disappointment or frustration.