grummeln

Etymology
From Low and Central German dialects, from and northern, iterative of. A relation with and  is theoretically possible, but the words certainly have a strong onomatopoeic element. Cognate with 🇨🇬, 🇨🇬.

Verb

 * 1) to grumble make a low sound, as of a discontent person, an empty stomach, a distant thunderstorm