Hey, I was experiencing the same problem, also with narration. When I switch to the "speech" compression format, the squeal is lost, but the audio quality becomes very poor, with lots of static.
Just so you all know, the squeal is not audible over the speakers, only on headphones, but since we expect a large portion of our audience to be using this project with headphones, this is a serious issue for us.
After some testing, I found that setting the quality to 64kbps got rid of the squeel, and increased the file size about 75%
Mainly, I believe this issue simply has to do with the quality of the original audio file. Although you may not hear any problems with the original file, if it was recorded poorly, underlying problems will be amplified when Flash compresses the file. I suggest getting a high-quality mic, and doing a proffessional recording session. Since we got a better mic, we havn't experiences this problem again.
Last edited by Rocketboy; 08-20-2007 at 09:02 PM.