My 5 month old does the same thing, it's truly ear piercingly painful. A midwife i know assured me its normal but my dd definitely does it more when tired. The only thing I find helps sometimes is to distract her by my singing....which may be where she picked it up to begin with though...:0
I know you don't want to hear this, but it is a phase. DD is 7m and doing this, and I watched all the other babies at the groups I go to go through the same thing at the same age. It lasts about a month.
I know what you mean about it being painful though. It is like my brain has been flossed!
Maybe get her checked out - for any physical problems - with the GP first.
Assuming that is ok, I would consistently ignore (again and again and again) and I wouldn't raise an eyebrow or react to it in any way. She must be associating making the mouse with getting some sort of attention (good or bad) and the only way to stop it is to not give it any attention at all. Doesn't necessarily mean "ignore her" (since she doesn't have many options of communicating at that age), just don't pay any attention to the noise.
6mo DD makes this high pitched scream/squeal/screech, which she picked up somewhere around 4mo. She goes through phases of using it a lot -- and has just entered another one. She did it throughout most of the day yesterday and just started up again this morning. I'm not sure, but I think it indicates some kind of distress: she often does it when she's rolled over on her tummy and is frustrated at her inability to crawl, or when she is very tired and resisting sleep. Yet she also often seems happy -- she screeches and then looks over at me with a smile.
The sound is actually physically painful. I love my DD, but when she makes this noise all I want is to get as far away from her as possible. How can I get her to stop? I've tried trying to fix anything that might be wrong -- changing a nappy, feeding, putting her back to sitting or her back (this last doesn't work at all -- she rolls back to her tummy immediately), picking her up and hugging her. I've tried saying a stern "No"; I've tried ignoring her; I've tried whispering to her or blowing bubbles to try to get a different sound. Nothing seems to work for more than a minute or so, if that.
I think she might be teething -- yesterday I gave her calpol thinking she might be in pain, but it didn't seem to help. She likes teething toys, but screeches around them.
Any advice? I'm not sure how I'm going to make it through another day of this...