If you loosen the screws, then eventually the vibration of the drive will completely unscrew them. This, of course, could make your hard drive fall or slide around (not good.)
Are you saying that your HD makes so much vibration that it can move the screws while the HD is resting on the said screws due to vibration alone? If this is the case, I'd suggest you buy a new HD first since this is definitely not going to help you! Nor would this help any suspension system listed here since the HD would probably vibrate right out of it.
The HD's weight alone resting on the screws in my case prevent any sort of screw movement at all. I could see this being a problem if i constantly transported my case from one location to another, but my case never moves from it's current spot. But of course, this goes with any of the other suspension systems listed here too and moving the case around.
PS. Just checked out your HD rack. I wish I had the room for something like that in this box.
PPS. I should also mention that I do not have the screws screwed only half way on (I should be more clear) and they are screwed against the mounting rack, just not 'tightened'. I find that when they are tightened, I get all the noise transfer.
I've been a Sys Admin/IT Director for many years.
In that time, I can't count the number of times I have opened up a computer to work on it and found some or all of the hard drive screws had loosened themselves
. In some cases, this caused the hard drive to be completely free of the chassis.
In these cases, no one purposefully untightened the screws, they just worked themselves loose, over time. This will happen because of vibration and also the expansion of contraction of metal as it is heated and then cooled (what is commonly called 'chip-creep'.) I have seen the same thing happen on computers I have built, over the years. I had tightened the screws, but some of them worked themselves loose, over time.
I know it sounds far-fetched, but it really happens.
This is why I do not recommend partially tightening hard drive screws. In my opinion, if you are going to use hard drive screws, then you need to tighten them well and use locking screws (the ones with ridges that help keep the screws from unscrewing.)
Of course, from a Silent PC persective, you really can't beat some kind of mechanical decoupling, such as the various suspension techniques or sorbothane.