My boxer grinds her teeth

Hi,

In the past 3 weeks my 5 yr old female boxer has started to grind her
teeth. It doesn't happen all the time just when she seems to be
relaxed. She will sometimes smack her lips together and the grind her
teeth. I had her to the vet and the vet says that her teeth look fine
and that she reacts the same way on each side of her face to stimuli.
She gave me a rx for acid reflux and said to try that.

Any light that you can shed would be appreciated.

Jason