(n.) A humming sound; a booming.

balmy birring blooming blossoming bombilation bombinating bombination boom burring buzzing cannonade cannonading clear deafening droning ear-piercing ear-rending ear-splitting earthshaking echo echoic echoing exuberant fair fat flourishing flowering forte fortissimo fruiting full fulminating going strong growl growling grumble grumbling halcyon hum humming in full swing in good case lingering loud loud-sounding loudish low rumbling palmy peal pealing persistent piercing piping plangent prospering prosperous purring reboant reboation rebound rebounding reecho reechoing repercussive resound resounding reverberant reverberating reverberation reverberatory ringing roar roaring robust roll rolling rosy rumble rumbling sleek sonorous sounding stentoraphonic stentorian stentorious thrifty thriving thrumming thunder thundering thunderlike thunderous thundery tonitruant tonitruous undamped vigorous volleying whirring whizzing window-rattling