Right, I understand! Apoligize for going ahead of things.
Webshops' verdict is out: OCZ3P1333LV6GK is NOT compatible with GA-X58A UD3R 2.0 even though it IS on the QVL! And that's after receiving TWO confirmed broken kits. The third kit was tested on several other motherboards, in which it worked fine. As for the motherboard, they could not hear any coilwhine, even though the whole setup was tested extensively. But at the same time, they also did not run into any other (extra) problems with it. But quite frankly, the coilwhine is not the biggest problem right now as the memory part turned out... good;
The webshop will swap the OCZ memory for a different kit, they suggested KHX1600C8D3K3/6GX. Which is not on the QVL, but if it has been tested by the shop and found 100% working, it doesn't matter (have contacted them about this, awaiting answer). As second option, I could also go for TR3X6G1600C8 which is on the Corsair compatibility list for this board. This whole deal is very kind of them, because this third kit was not purchased from them, but from OCZ RMA strictly speaking. So they aren't even obliged to take back the OCZ kit and have it swapped for me without extra costs, but they did so anyway! They managed to work out a deal with OCZ, for which both parties deserve and got my thanks.
About the coilwhine again, I will ask the shop for a summary on how they have tried to reproduce it and with which hardware. PSU, RAM, CPU, GPU, voltages, HDDs and whatever. I'd like to know it all. It doesn't feel quite right that they haven't heard anything. Not that I distrust them, but it was so easy to reproduce back at home. Any thoughts on this are still welcome, though by now everything has probably already been said.
And I have kindly asked OCZ and Gigabyte to retest this kit on this specific board