At least 10 distinct vocalizations have been identified: snorting, honking, bleating, roaring, squeak-panting, moo-grunting, shrieking, groaning, rumbling and humphing.
en.wikipedia.org If it is harassed further, it will twitch in an attempt to jab spines into the predator and make snuffling/grunting noises.
en.wikipedia.org The whirr of the engine, the shove in the backside and the little roadster that seems to pivot around you is replaced by a grunting, belching, feedback-free driving experience.
en.wikipedia.org Once the two meet, the man is horrified to observe that his date is masculine, grunting, and lurching.
en.wikipedia.org