Piercing cry rocks church (7)
I believe the answer is:
screech
'piercing cry' is the definition.
(a screech is loud or shrill cry)
'rocks church' is the wordplay.
'rocks' becomes 'scree' (rocks on the slope of a mountain).
'church' becomes 'ch' (common abbreviation).
'scree'+'ch'='SCREECH'
(Other definitions for screech that I've seen before include "Loud harsh cry" , "Sudden shrill cry" , "Raucous sound" , "Sharp piercing cry" , "Squeal" .)