Noise levels were measured with an Extech 407727 Digital Sound Level meter 1" from the side of the drives at idle and under an HD Tach seek load. Drives were run with the PCB facing up.
42.6 decibels is the ambient noise level of our test system, and the mechanical drives don't add a lot to that at idle. Honestly, even at a couple of feet away from a bare drive, my ears couldn't hear the difference between the Momentus 7200.4 and the Spinpoint M7.
Under a seek load, the drives start to make audible noise. Some of them do, anyway. The Scorpio is the quietest of the lot, with the Spinpoint and Travelstar a couple of decibels louder according to our sound level meter. My ears have no problem detecting more audible clicking with the Momentus drives, which are the loudest of the bunch.
For our power consumption tests, we measured the voltage drop across a 0.1-ohm resistor placed in line with the 5V and 12V lines connected to each drive. We were able to calculate the power draw from each voltage rail and add them together for the total power draw of the drive.
We don't see huge differences in power consumption between the five mechanical drives. The 7200.4 requires more juice, of course, but the difference isn't of nearly the same magnitude as the step up in spindle speed. Hitachi proves to have the best power efficiency of the mechanical bunch.