Loose rocks by church make an unpleasant sound (7)
I believe the answer is:
screech
'an unpleasant sound' is the definition.
'loose rocks by church' is the wordplay.
'loose rocks' becomes 'scree' (I've seen this before).
'by' means one lot of letters go next to another.
'church' becomes 'ch' (common abbreviation).
'scree'+'ch'='SCREECH'
'make' is the link.
(Other definitions for screech that I've seen before include "Terrifying sound" , "cry of horror" , "Squeal" , "Sudden shrill cry" , "Shriek" .)