Many words in English (and other language) are a reflection of natural sounds (or our interpretation of natural sounds) – onomatopoeic words. Frogs croak, cats meow, horses whinny.
Quite a few words in English reflect the sound of frustration or discontent – grrrr. Think of words such as grumble, grunt, growl, grouch and grudge. Groan comes from Old English grorn (meaning sorrow) and grief comes from the Old English gretan (to weep).
Grin, which today we associate with a mischievous smile used to mean ‘to scowl’ or ‘to show your teeth in anger‘. Greet, which today also has positive connotations, once meant to ‘call upon’, ‘cry out’ or ‘assail’.
Grr also represents the sound of a grinding wheel which grinds particles into smaller substances – grit!
Reference
Liberman, A. (2009). Word Origins. Oxford University Press: NY