Ripping files and backups do not match?

Hello all,

  I am in the process of ripping my cd collection to flac using dbpoweramp.  I am using my Dell laptop for the initial rip and then copying to two Seagate usb hard drives.  I was running out of room on the laptop hard drive so after backing up to the usb drives, I noticed the drives do not have the exact same amount of data in the music file.  There is 32,768 bytes difference.  I recopied both drives from the master file and the difference still exists.  The file count is the same and all artists and songs are the same.  Is this something that happens during the rip?  Should I be concerned?  Both discs play fine on my digital player and sound quality is equal.  I have over 1,000 cds and this is a very time consuming chore.  I just want to make sure I'm not messing up.  Thanks for any info or suggestions.