>>It may be that the tortoise is clicking its jaws together, or actually snapping the lower beak on the upper beak. You can approximate this sound yourself by pulling your thumb nail over one of you other fingernails on the same hand. In some tortoises, it can indicate that the beaks are getting overgrown. It is the tortoise's attempt at wearing the beaks down to make them have a proper bite.
That's basically what I was thinking. It could be the signs of a beak beginning to overgrow. If that's not it sometimes there are some who are just noisy eaters. I have a couple of box turtles who have always made clicking popping noises when they eat.
You might want to check the mouth because there was one instance with one of the box turtles- she kept doing this, kept doing it wouldn't stop so I checked her mouth & sure enough she had food stuck in her mouth that she couldn't swallow & couldn't spit out. I pulled it out for her & it stopped.
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PHRatz