grumble about (someone or something)
To complain or gripe about someone or something. I turned the thermostat up, so you all can stop grumbling about how cold it is in here, thanks. Of course Marjorie is grumbling about how I left dishes out in the kitchen—she's not happy unless everything is perfectly put away.
grumble about someone or something
to complain about someone or something. What are you grumbling about now? The students were grumbling about the teacher.