little | low | non-committal
He gave a non-committal grunt in reply.

give, let out | hear

with a ~
He lifted the heavy box with a grunt.

~ of
a grunt of pain

loudly | merely, only
He merely grunted at her and nodded his head.

at
His father grunted at him as he left the room.

in
She asked him a question and he grunted in reply. | He grunted in pain.

with
She stirred the soup, grunting with satisfaction.

grunt and groan
Grunting and groaning, they heaved the wardrobe up the stairs.