Teeth grinding when being saddled, what is this noise?

I have a 9 year old OTTB that when you are tightening the girth, he makes this weird grinding sound with his teeth, or like he scs his teeth together, it makes kind of a squeeking noise. And sometimes when he's standing tied to be saddled, he'll keep trying to chomp on the tying post. I was fearful these were possible signs of cribbing? I'm not that familiar with it though, should these noises with his teeth be something I should worry about? and how do I stop him from chewing? for I think sometime in his racing career he may have been hit a lot with a whip or something cruel, so I can't smack him and tell him no or he'll pull on the rope and get horrible freaked out if things move that quick by his face. suggestions?