Well rob if it's anything like HDD's in pc's then yes they can whistle i have had pc's with the same hard drives in them and one would whistle and one would not.
I have had a DMR-HS2 now for a fortnight. There is a minimal amount of whistle from the hard drive but it certainly is not excessive. in fact the hard drive noise is less than that of my sky+ box or the Tivo recorder. perhaps if Automan isviewing these forums he might like to pass his opinion as he is well versed with all of these hard drive recorders
I have the advantage of having my unit in a cabinet with glass doors underneath the television. however with the doors open and the television turned off, my machine, which is currently dubbing from ram to hdd,can be heard from across the living room if everything else is in total silence.
I dont know if you have any other experience with hard disc recorders, but it is a feature of their operation that you can hear low pitch noise.
The HS2 has no still frame advance,this was very useful for doing accurate edits.It also doesn't have the same picture adjustment (colour,brightness,contrast etc) as the DMR-E20,also I think the DMR-E20 was much classier with it's aluminium front panel,the HS2 looks cheaper.
It's a Maxtor D540 HDD 5400rpm and fairly noiseless, but they all make some noise
and it can't be upgraded to anything larger as it's in the firmware fixed at 40GB (Although it will work with a bigger drive it just will only use 40GB of it)
Rob: You can do frame accurate editing on the HS2. When in partial erase for example, press scan fwd until you get to approximately the edit position. Hit pause, then fwd or reverse to step through one frame at a time. I've found you can get really accurate edits this way.