Ubuntu :: MD5 Sums Of Files Keeps Changing?

I copied files from one hard drive to another so I made md5sums of the files to make sure everything went okay. They don't match. I wrote a quick bash command to compute the md5sums of all the files and save the result. Half of the time I get something different.

Code:

x=1;while [ 1 ]; do nice -n 8 md5deep -r -l copy > md5.of.copy.$x; x=$(($x+1)); done

It's not just on ntfs. A different hard drive with an XFS filesystem shows the same thing happening.I was wondering if my memory is corrupt so I did a quick test:

Code:

while [ 1 ]; do nice -n 8 dd if=/dev/zero bs=1G count=1000 | md5sum >> dev.zero.log; sleep 5m; done

Same result every time. No errors.