grumbling

Adjective

• continuous full and low-pitched throbbing sound
  • the rumbling rolling sound of thunder
    

Noun

• a complaint uttered in a low and indistinct tone

• a loud low dull continuous noise
  • they heard the rumbling of thunder
    

Related words

• Synonyms: 
  rumbling , grumble , murmur , murmuring , mutter , muttering , rumble