Warning about echo in that place (7)
I believe the answer is:
thereat
'in that place' is the definition.
'warning about echo' is the wordplay.
'warning' becomes 'threat' (threat is a kind of warning).
'about' indicates putting letters inside.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'threat' going around 'e' is 'THEREAT'.
(Other definitions for thereat that I've seen before include "On account of that" , "Theatre (anag)" , "At that point" , "At that place" .)