grommeler (ww):
grommelen(fr) —.
(en) to murmur or mutter with discontent., morren(fr) —.
(en) to murmur or mutter with discontent., mopperen(fr) —., grommen(en) to utter a deep guttural sound.
(en) to murmur or mutter with discontent., mompelen(en) speak under one's breath.
Via: Dbnary en WikiWoordenboeken
Via: Memodata.com