grumbling

/G R AH1 M B AH0 L IH0 NG/
verb
  1. 1

    To make a low, growling or rumbling noise, like a hungry stomach or certain animals.

    โ€œThe distant thunder grumbles.โ€

  2. 2

    To complain; to murmur or mutter with discontent; to make ill-natured complaints in a low voice and a surly manner.

    โ€œHe grumbles about the food constantly, but has yet to learn to cook.โ€

  3. 3

    To utter in a grumbling fashion.

noun
  1. 1

    Complaining

    โ€œthe grumblings of a bad-tempered manโ€

  2. 2

    Rumbling

Source: https://en.wiktionary.org/wiki/grumble, https://en.wiktionary.org/wiki/grumbling