Audio data varies from drive to drive?

Hi,

Out of curiosity I ripped the same track on three different 
CDROM-drives, for two different discs. Each time I used the command 
"cdparanoia 1". The ripping went with no error in each case.

I noticed that the resulting cdda.wav files are different from drive to 
drive. When I look at the files in vbindiff I can see that the 
differences are scattered throughout the files. For example at a given 
offset, one file will have a byte value of 0x00, the other will have 
0x01 -- the differences seem to be small, although I have seen sometimes 
0xff instead of 0x00.

I would expect the audio data to be identical regardless of the drive 
which does the reading. Am I doing something wrong?

I'm happy to provide the drive specs if you need them.