Mouth Quivering ( shaking ) ?? help?

[delspf]

HI

Having a problem with my dog, all a sudden today his mouth is going nuts. Like his bottom jaw keeps "shaking". You know how dogs look when they act like they are "Talking" well his bottom jaw is doing that movement...and constantly, like quivering.

Can't find anything about it online because I don't know exactly what to search for...anyone have any ideas?

Austrailian Shepherd and about 13-14yrs old. Very active for his age, sure doesnt seem to be that old.