My current mini has ddr3 and has the hdd heat sensor.
My last mini was ddr2 and did not have the hdd heat sensor.
But now that it has been a few days with no problems since the upgrade.
I think that the very slight whirring that I still hear is just the hard drive spinning, it is a 7200 rpm so I would imagine it might make just a little noise.
I can barely hear it if the room is dead quiet, so I can live with that.