Noticed trouble is deep (6)
I believe the answer is:
espied
'noticed' is the definition.
(I've seen this in another clue)
'trouble is deep' is the wordplay.
'trouble' is an anagram indicator.
'is'+'deep'='isdeep'
'isdeep' is an anagram of 'ESPIED'.
(Other definitions for espied that I've seen before include "Caught sight of (poetic)" , "Saw (archaic)" , "Watched" , "Spotted; saw" , "Caught sight of (archaic)" .)