Deep sound (4)
(Other definitions for boom that I've seen before include "sound of artillery fire" , "Spar - loud noise" , "Noise of large explosion" , "Prosperity - hollow roaring noise" , "Crash" .)
(Other definitions for rumble that I've seen before include "Deep resonant sound - discover an illegal activity" , "Fight between rival gangs of adolescents" , "Low continuous noise" , "Discover the truth about" , "street-fight between gangs" .)