Audible Noise Levels
Tthis is one of those aspects where the HD1000U could be slightly better. In low power mode, it is certainly quiet enough, even those who are the most noise intolerant should not have an issue. Run the HD1000U, though, at full power and it's not going to please those same people. The noise level, claimed to be 31db at full power, is not by any means excessive. Most people will never notice it while watching a movie, unless they are listening for it. The sound is low pitched, and even as you notice it (listening for it), as you settle into your movie, you may notice it in quiet scenes but it shouldn't be intrusive. So, concern is only for those who really hate hearing any fan noise at all, ever!
I would say that it is just slightly quieter than the HD72. On the other hand, The Panasonic PT-AX100U is definitely quieter in both full and low power modes.