Small dog yelps when startled or someone moves

She's a yorkiepoo and less than ten pounds. When you're sitting next to her and move positions or stand up, she yelps. If she is startled, she yelps.

I always thought it was because she's so small and she's trying to remind you that she's there so she doesn't get stepped on or sat on or something.

it's very abrupt, loud, and high pitched, though. It can hurt my ears. She'll do it at night, when people sleep, in public, or right in your ear. It can be very disruptive.

I've tried ignoring it. I've tried telling her to be quiet which is a command she usually understands. She is six years old and this is not new. She is not in pain, injured, or need a vet. She is healthy and has regular checkups.

Is there a way to get her to stop?