Definitely discuss this with your pediatrician. Actually it sounds more like a nervous tic, and she can't stop doing it because once those things start, it's hard to stop. Has she started nursery school recently, or did she start something new?
At times a change in routine and a stressful situation can create some sleep issues as well as nervous tics. My oldest son had a throat clearing tic, and he always started it early in the school year. It tended to resolve as the year went on and he adjusted to his classroom.
I wouldn't jump to the GERD conclusion, although of course, it's possible. Your pediatrician will know what direction to take this in. If it were a tic, the trick is ignoring it. Bringing attention to the behavior only makes it worse.
Good luck figuring it all out!
Let us know what your doc says.
Words of wisdom by Eckhart Tolle:
"Whatever you fight, you strengthen, and what you resist, persists.”
“Worry pretends to be necessary but serves no useful purpose”
“Accept - then act. Whatever the present moment contains, accept it as if you had chosen it. Always work with it, not against it.”