I've seen this happen once, I'm not sure what caused it for sure, but the power supply was going in the machine at the time. A reboot fixed it, and I've never seen it again (the PS was replaced while it was shut down, so I didn't get a chance to test if that was what was causing it or not) Every file on the system when you read it, would randomly show weird characters like you describe. It didn't matter what the file was.