The stones make alarming sound, putting last couple off (5)
I believe the answer is:
'the stones' is the definition.
(scree is a mass of loose rocks on a mountain)
'make alarming sound putting last couple off' is the wordplay.
I cannot quite understand how this works, but
'make' could be 'cree' (I've seen this in another clue) and 'cree' is located in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for scree that I've seen before include "Loose stones around a mountain" , "Talus" , "Loose shifting stones" , "bits of rock" , "Stony hillside" .)