I imagine most of the noise these drives emit is from the disturbance caused by the disc spinning - so make a very slow drive (15x for a CD? That's less than a third of the speed of most drives nowadays) and it will be quieter. I wonder what speed conventional drive they are comparing this with.

Notebook drives may also be noisier due to their size - there might be less physical screening. The comparison should be with the same form-factor of drive, to make it fair.