An unreasonable adversary, such as a terrorist group or something, could plausibly do that. But the legal system has things like the "beyond reasonable doubt" standard of guilt. If the court finds encryption headers on your disk, they've got evidence beyond reasonable doubt that there's encrypted data on it. If there's only noise, it's totally plausible that it's just a spare usb stick, especially if you consistently wipe your unused disks and don't just have one conspicuous disk full of noise.