かっかっかっかっ这个象声词是什么意思

Japanese language has rich expression of 役割语. Particular expressions explain their gender, age or social title.
In case of a sentense you mentioned,
"良いのう 良いのう"
→"のう" is old-man's saying.
→"おミツ" he just say "おミツ" , not to add "さん" or "さま" like that. Although "お" of "おミツ" express a slight politeness, not adding "さん" means he will be old and her family, or he is very high-lanked person like 水戸黄门.
In most case, he is her father or grand father.

→"かっかっかっかっ"
This is a particular words to express old-man's laughing.
I'm doubt that it came from Chinese expression in old textbook "呵呵大笑". "呵呵大笑" is pronounced as "kaka taishou" in Japanese 音読み. "kaka" is a sound of laughing, and in Japan, it turned to express only old man's laughing.

追记：
「かっかっかっかっ」は、老人が何かに満足して大声で笑っている様子です。