Well that is interesting. Usually the low speeds make for better audio CDs.
I do question the need for them in this age of MP3, FLAC, etc and solid state players like ipods and smartphones.
One guess might be dirty power. If the power supply is misbehaving, either internally, or itself is getting dirty power, then I could see an optical drive having trouble staying consistent.
You could fire up a voltage monitoring tool like Hardware Monitor and see if the voltage is doing anything weird.
Another guess would be bad data cables or high levels of electrical noise in the system. A little more difficult to troubleshoot. If you have any spare SATA cables, swap it out. If this is an external drive, well, not sure, you could get some metal mesh and have that around the drive and cables.