Hearing sounds echoing, circling valleys finally (7)
I believe the answer is:
session
'hearing' is the definition.
(I've seen this before)
'sounds echoing circling valleys finally' is the wordplay.
'sounds' becomes 'noises' (noising is a kind of sounding).
'echoing' shows that the letters should be reversed in order (echo can mean to reflect).
'circling' is an insertion indicator (circling can mean going around or containing).
'finally' says to take the final letters.
The last letter of 'valleys' is 's'.
'noises' backwards is 'sesion'.
'sesion' enclosing 's' is 'SESSION'.
(Other definitions for session that I've seen before include "Fifty minutes lying on a couch" , "Period of business for official body" , "Parliamentary period" , "Meeting or series of meetings" , "Period devoted to an activity" .)