Onset of loud din rising will cause hurt (6)
I believe the answer is:
lesion
'hurt' is the definition.
(I know that lesion is a type of hurt)
'onset of loud din rising' is the wordplay.
'onset of' suggests taking the first letters.
'din' becomes 'noise' (a din is a noisy disturbance).
'rising' says the letters should be written backwards (letters written upwards in a down clue).
The first letter of 'loud' is 'l'.
'noise' written backwards gives 'esion'.
'l'+'esion'='LESION'
'will cause' acts as a link.
(Other definitions for lesion that I've seen before include "A cut or wound in insole" , "Kind of injury in insole" , "Damaged area of tissue" , "Damage to tissue from injury or disease" , "Abrasion" .)