[tlrobinson]

I think on most operating systems the free space usually contains remnants of deleted files, not random data, unless you use some sort of secure deletion mechanism (srm, etc). If the free space of your volume contains truly random looking data then there would be reason to suspect a hidden volume.

Presumably that's not the case with TrueCrypt volume-within-a--volumes, but if you're using TrueCrypt there's already reason to suspect you might have hidden volumes.

It's impossible to prove the existence or nonexistence of hidden volumes, but that could be a good or bad thing depending on your adversary's willingness to jail/torture/kill you on suspicion alone.

I'm not aware of hidden volume software that integrates with "unsuspicious" file systems. Does something like that exist?