My Google-fu has been useless here, and my knowledge of low-level storage details is terrible.
Does a brand-new, right-off-the-shelf hard drive contain all random noise, or do they come with all zeroed-out bits? I've wondered for a while but it's mostly been a question to consider in passing. This may be a manufacturer-specific detail, however.
For context, I was considering whether or not an encrypted section of a disk would be identifiable by an adversary. Secure ciphers are (conjectured to be) indistinguishable from random noise, and so if new drives were all random noise, an adversary would be unable to identify an encrypted section. If new drives are all zero bits, however, it would be precisely the opposite.