Could my molars be cracked under the crown?

I started experiencing pain on lower right where I have two crowns - one had a root canal long ago. The x-ray and other tests came up blank. The pain's location is confusing as it extends to other teeth which are fine. The crowns in the back look fine, and seems to me that the tooth that with the root treated is more sensitive. Could it be that any of the molars have been cracked under the crown? I have bruxism, but this pain is way beyond that.