As a follow up to my post-install COBB springs concern, I contacted Dave from nasioc who owns same car with same springs and asked him whether he experiences same noise as do I. I was happy to find out he has same "symptoms". It's kind of good and not at same time. Good because that means everything is fine with my install. Bad because I don't think I'll get used to the noise as he did. I will quote him:
I also have a noise up front when I go over bumps. It is more like a rattle correct? A slight metal to metal sound? I am not sure what it is, but the only thing I can think of is that maybe the spring is short enough that when uncompressed it becomes loose and rattles slightly. It bugged me at first and now I don't even notice it anymore.
Dave
In the meantime I contacted my vendor and asked to check with COBB about this.