Deep resonant sound (6)
'deep resonant sound' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rumble that I've seen before include "Carriage seat gives the sound of heavy wheels" , "Low, vibrating (traffic) noise" , "Sound of distant thunder" , "gang fight in New York City?" , "Make a continuous resonant sound" .)
'deep resonant sound' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for boom that I've seen before include "Resonant sound < of TV equipment" , "Prosperous time - sound of explosion - yachting spar" , "Loud noise - business increase" , "Crash" , "Report" .)