Experts, quiet ones, impress department (7)
I believe the answer is:
pundits
'experts' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps there's a link between them I don't understand?
'quiet ones impress department' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'ones' becomes 'units' ('unit' can be a synonym of 'one').
'impress' is an insertion indicator (impress can mean enlist or recruit).
'department' becomes 'd' (this might be a standard abbreviation I've not previously seen).
'units' going around 'd' is 'undits'.
'p'+'undits'='PUNDITS'
Can you help me to learn more?
(Another definition for pundits that I've seen is " Authorities on particular subjects".)