Overact before noon in greeting sheepish mate? (3,2,2)

I believe the answer is:

ham it up

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'overact' is the definition.
(I've seen this before)

'before noon in greeting sheepish mate?' is the wordplay.
'before noon' becomes 'am' (as in AM on a clock).
'in' indicates putting letters inside.
'greeting' becomes 'hi' (hi is a kind of greeting).
'sheepish mate?' becomes 'tup' (both can mean to copulate. I am not sure about the 'sheepish' bit.).
'am' inserted within 'hi' is 'hami'.
'hami'+'tup'='HAM IT UP'

Can you help me to learn more?

(Another definition for ham it up that I've seen is " Overact".)

I've seen this clue in The Independent.

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