I think watercooling will be the quitest, most effective solution.
Gaming PC usually has at least 3 case fans, 1 or 2 CPU fans, PSU fan. That said, I can definitely hear my HDs above the fans (more the sound of moving air, to be precise).
A good investment is always good fans, and case insulation to stop vibrations. Heck of a lot cheaper than watercooling, though far less effective.