A racy sort of utterance (5)
I believe the answer is:
vroom
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for vroom that I've seen before include "Sound of a car speeding away" , "roar away" , "(Of engine) make roaring sound (colloq.)" , "Fast revving sound" , "Sound of an engine revving" .)