Do any terrestrial herbivores use auditory crypsis for predator avoidance?
Does soundproofing count?

Most predators locate prey using visual or olfactory cues; the only predators I can think of that use auditory cues are nocturnal ones - owls and bats. Bats, of course, use echolocation, so even completely silent prey are still detectable. It has been suggested that the soft, fur-like body coverings of some owlet moths (Noctuidae) and tiger moths (within the Arctiinae) help hide them from echolocating predators by passively absorbing sound, although subsequent studies have suggested that they may instead be mimicking the acoustic signature of unpalatable prey.


(public domain image: source)

I have a suspicion this isn't what you meant by 'land-dwelling herbivore', but insects are people too...

Edit: just discovered this paper from May that provides evidence supporting the hypothesis that the twisted tails of luna moths (Actias luna) disrupt tracking by echolocating bats.


Image owned by Shawn Hanrahan, licensed under CC BY-SA 2.5