This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
Somebody described this as listening to songs recorded by Alvin and the
Chipmunks. What's happening is the software used to uncompress the MP3
files is doing a poor job, and the uncompressed data is effectively being
recorded at a lower sample rate. When the CD player tries to play it
back at 44.1KHz, it sounds like the artists are inhaling a crude mixture
of amphetamines and helium.
This has been reported with Easy CD Creator v4.05 and v5, NTI CD Maker 2000+,
and something called Orion Liquid Burn.
The work-around is to expand the MP3 files into 44.1KHz 16-bit stereo
PCM WAV files on your hard drive, and record from those instead of from
the MP3s. Use a decoder/player such as WinAmp (http://www.winamp.com/)
or a sound editor to convert the files.