I bought myself a new laptop three days ago, and lo and behold, it ain’t quite right–the optical drive buzzes like a B52 when a CD is running. It is much quieter when playing a DVD, though. Might this be because DVDs spin slower than CDs?
Also, is it absolutely clear that I’ll have to exchange my laptop for another, or might this be something I can fix myself, quickly and easily, without voiding the warranty?
Are you playing an ordinary audio CD at 1x rate or a data CD that may be spinning at maximum rate? I honestly don’t know what the 1x spin rate is for both but that may account for what you’re seeing.
Does it happen with all CDs? This is often a consequence of the disk being unbalanced by something as little as the label design having more ink on one side than the other.
The 1x rate for CDs and DVDs is about the same, between 200 and 500 rpm.
However, computer CD drives are much, much faster than DVD drives. The fastest CD-Rom drives can go up to 58x, or 29,000 rpm (which is actually dangerously fast, as Mythbusters proved) while the fastest DVD-Rom drive on the market is only 16x – and if your laptop is over a year old, it’s likely only a 4x or 8x drive.
In other words, there’s nothing wrong with your laptop. This is normal. 
Some CD/DVD drives have built-in vibration sensors. This allows them to automatically reduce the motor speed when an out-of-balance CD or DVD starts making noise.