Terrifying sound rocks church (7)
I believe the answer is:
screech
'terrifying sound' is the definition.
(I've seen this before)
'rocks church' is the wordplay.
'rocks' becomes 'scree' (I've seen this before).
'church' becomes 'ch' (common abbreviation).
'scree'+'ch'='SCREECH'
(Other definitions for screech that I've seen before include "Raucous sound" , "Squeal" , "Loud harsh cry" , "cry of horror" , "Sudden shrill cry" .)