Gosh, they do make an unholy din! (5,5)
I believe the answer is:
hells bells
'din' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for hells bells that I've seen before include "Those with a ring of fire" , "dammit?" .)