What cows do with Mark is not nice (3,4)

I believe the answer is:

low note

'is not nice' is the definition.
(a low note is something unpleasant)

'what cows do with mark' is the wordplay.
'what cows do' becomes 'low' (low can mean to make a mooing sound).
'with' says to put letters next to each other.
'mark' becomes 'note' (mark can mean to note or remember).
'low'+'note'='LOW NOTE'

I've seen this clue in The Guardian.

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