They may carry sleeping bags, we hear (9)

'they' is the definition.
Both the definition and answer are plural nouns.
Maybe they are linked in a way I don't understand?

'carry sleeping bags we hear' is the wordplay.
I cannot really understand how this works, but
'sleeping' could be 'nap' (nap is a kind of sleeping) and 'nap' is found within the answer.
'bags' could be 'sacks' (sack is a kind of bag) and 'sacks' is found within the answer.
A single letter 'k' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'may' is the link.

Can you help me to learn more?