Why does my mp3 audio sound like a chipmunk is talking?

When audio files are not encoded at the correct speed, the Macromedia Flash player can play at double speed. When it is played at double speed, it causes everything to sound high-pitched - and resulting in sound that is sometimes called the "chipmunk effect".

To prevent the "chipmunk effect", audio files need to be encoded at a rate that is a multiple of 11.025 kHz.

MP3s should be properly encoded at 11.025 kHz, 22.050 kHz, or 44.100 kHz.