Hi Paul,
It sounds like she is doing an alarm call. This may have started when she saw something that scared her – maybe something outside if she is near a window or something new in the room. But by getting attention, this encourages her to continue it. Any type of attention is a reward, so the best thing to do is to ignore the sound and then pay attention to her when she is quiet or making regular sounds. If she is not a tame bird, she may simply be lonely because parakeets do live in large flocks. She may be hormonal and wanting a mate. I’m not suggesting you have to get another bird, but it might help to get her a companion if you do not handle her. If you do handle her, maybe you have not been handling her enough. You can try more toys and maybe relocating the cage just to change her routine a bit. But again, completely ignore the unwanted noise because even covering her or telling her to stop or doing anything to try to distract her is a reward and will just encourage her to do this more.
Thank you for asking Lafeber,
Brenda