Produced a sound by forcing air through the lips (8)
I believe the answer is:
whistled
'produced a sound by forcing air through the lips' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for whistled that I've seen before include "Signalled the end of a match" , "Indicated foul" , "Catcalled" , "Produced a sound by forcing air through the lips" , "Made a sound like steam coming out of small aperture" .)