At 12v, they're not totally silent, there is wind noise- I have removed all finger guards as well (one on each side) At 7v it's silent, but airflow is basically non-existant, not enough to expel air from several hot components in the case. The HD mountings are solid so vibrations/noise isn't dampened. I've used window sealent strip between the HD cage and case, and strips of bicycle inner tube between HD and cage. Helped reduce noise. The problem with this case is HD cooling, the one at the bottom (pic) is suitably cooled but I placed another drive above that in the cage and that got considerbly hotter, hot enough to move it elseware. At the moment it's on the case floor ontop of more rubber strips. It's much cooler as it has direct airflow over it from the front case fan.
I've used the Antec NSK 2400 (desktop style MATX) and that was a lot better in cable managment and general fit/tidyness (the holes on the side and front panel really do help) however I haven't compared HD temps as the HD bays have no airflow, except natural air convetion. I've used a Qpack and that was horrible, much worse than the Silverstone (cannot fit large VGA cards or CPU fans, everything is squidged close together)
Would I buy this case again if I needed a MATX micro tower? Yes. It's not perfect though and some things can be improved (but so can my stacker, HD fitting/removing requires HD modules & faceplates to be removed) Silverstone should have included HD mountings/cage on the case floor, and used HD isolation. The case could do with being 1" deeper to reduced any PSU-Optical drive issues. I guess you could thread tap some holes on the front for a additional HD cage bay, or you could use Lian Li MF-20/30 HD side plates to lower HD placement.
Since this'll be a gaming machine I would just buy a full tower setup installing stuff into my stacker is a joy compared to MATX...and temps are lower in every regard.