Sound of Bertrand in speech? (6)
I believe the answer is:
rustle
'sound' is the definition.
(rustle is a kind of sound)
'bertrand in speech?' is the wordplay.
'bertrand' becomes 'russell'.
'in speech?' shows a homophone (sound like) (I've seen 'in speech' mean this).
'russell' is a homophone of 'RUSTLE'.
'of' acts as a link.
(Other definitions for rustle that I've seen before include "Steal (cattle, etc)" , "Steal cattle or livestock with whispering sound" , "Low sound of rubbing" , "Dry crackling sound" , "Swish - steal cattle" .)