does anybody notice some clicking noise mostly coming from the back (sometimes from the front also but relatively rare) after the installation of the SPT suspension kit? (it's a factory option)
this is noticeable when cornering hard and/or going over speed bumps.

a friend said it could be that the struts put much more vibrations to the top mounts and thus the noise. If this is true, is changing the top mounts a way to resolve this problem?

 

I haven't noticed any clicking with the STi struts and springs on my car. You might want to make sure everything is tightened down correctly. Just be careful not to overtorque the strut top bolts. They'll break easily.