Audible hidden watermarks? Would like to compare .AA files from Audible.

[RevRhubar]

I was wondering if anyone knew if Audible insert hidden customer-identifying watermarks into their audio books? I.e. when you download an .aa file is your account number or something merged into the file (as in Steganography)? So if a DRM-stripped version of the file ever found itself onto a p2p network Audible could trace the original purchaser of the file.

Not that I have any intention of uploading my files onto the Internet, but I like to convert them into old fashioned CDs (which are obvioulsy DRM free) and if they were lent/stolen and then illegally distributed, I could be liable.

One way to find out would be to get two copies of the same file purchased from two different Audible accounts and see if the files were identical (rather that sharing the actual .aa files we could each use a program to compute a 'hash' or something on each file and then compare the hashes).
Let me know if anyone is interested in doing this.