In that case, its new, tight fitting plates making it quiet. The problem with tight fitting plates is that they can bind in the basket slots though, which can lead to dangerous degrees of drag. Maybe he got the order of the plates wrong and did the quiet mod inadvertently... Lol
The preload on the springs is determined by the length of the bolts. Just wind the bolts in until you feel them bottom in the thread and no more. The pressure from the springs will prevent them from undoing and attempting to tighten them more will risk stripping the soft threads. You will need to push the bolts in against the springs each time to start the bolts in the threads but simply applying pressure with your Allen key in the bolt head will suffice.
Drop round mine over the weekend and we can play with your bits. I also have a massive tool if we need to take the hub off....