General Complaints:
* Mutter: To speak in a low, unclear voice, often complaining.
* Complain: To express dissatisfaction or protest.
* Whine: To complain in a weak or childish way.
* Moan: To express pain, sadness, or discontent.
* Grouse: To complain in a bad-tempered way.
* Kvetch: (Informal) To complain constantly and in a nagging way.
Sound-Related:
* Rumble: To make a low, continuous sound.
* Growl: To make a deep, guttural sound, often expressing anger.
More Figurative:
* Bemoan: To express sorrow or regret for something.
* Deplore: To express strong disapproval of something.
* Condemn: To criticize strongly.
The best synonym will depend on the specific situation and the tone you want to convey.