Crossword Genius

Suddenly said irrational youngster was hiding keys (5,2)

Ross

I believe the answer is:

piped up

I'm a little stuck... Click here to teach me more about this clue!

'suddenly said' is the definition.
The definition and answer can be both to do with communicating as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?

'irrational youngster was hiding keys' is the wordplay.
I cannot really understand how this works, but
'irrational' could be 'pi' (an irrational number) and 'pi' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for piped up that I've seen is " began to speak".)

I've seen this clue in The Daily Express.
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