I just received a 512 as a replacement for our ancient 510 that finally died. This 512 is very noisy -- can't say for sure if it's the hard drive noise or a fan. But the noise never takes a break, even when the receiver is off. It's a faint, higher-pitched noise that certainly is the kind of noise that grates on you and eventually causes you to do horrible things like chop the DVR with an axe in the middle of the night. Is this the nature of the 512 or do I have a bad one??? Thanks!