Hearing strange noises following start of stomachache (7)
I believe the answer is:
session
'hearing' is the definition.
(I've seen this before)
'strange noises following start of stomachache' is the wordplay.
'strange' indicates an anagram.
'following' means one lot of letters go next to another.
'start of' indicates taking the first letters.
The first letter of 'stomachache' is 's'.
'noises' with letters rearranged gives 'ession'.
'ession' after 's' is 'SESSION'.
(Other definitions for session that I've seen before include "Meeting or series of meetings" , "Bout" , "Court sitting" , "Period during which a group meets" , "Official sitting" .)