Notice saying 'Go Up and Down' (6)
I believe the answer is:
seesaw
'go up and down' is the definition.
(I've seen this before)
'notice saying' is the wordplay.
'notice' becomes 'see' (I've seen this before).
'saying' becomes 'saw' (saw is a kind of saying).
'see'+'saw'='SEESAW'
(Other definitions for seesaw that I've seen before include "entertainment for children" , "Rock unsteadily" , "Playground device" , "Fluctuating playground ride" , "Rise and fall" .)