Dope engaged by factory sounding mournful (8)
I believe the answer is:
plangent
'sounding mournful' is the definition.
(plangent can mean sounding mournful)
'dope engaged by factory' is the wordplay.
'dope' becomes 'gen' (both can mean information).
'engaged by' indicates putting letters inside (I've seen this in other clues).
'factory' becomes 'plant' (a manufacturing plant).
'gen' inserted inside 'plant' is 'PLANGENT'.
(Other definitions for plangent that I've seen before include "Noisy" , "Possibly ringing" , "Resounding" , "(Of sound) mournfully resonant" , "Loud and sad" .)