Mouse's sound (6)
I believe the answer is:
squeak
'mouse's sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for squeak that I've seen before include "indication oil's needed?" , "Shrill cry - narrow escape" , "Close shave - shrill sound" , "Pip's partner -- quakes (anag)" , "High-pitched animal noise - (narrow) escape" .)