Akurei

I have the same issue with my other car. It has h&r sport lowering springs with tokico hp blues. Sounds like my rear struts are loose. I checked every bolt and bushing possible in the rear, everything is tight and within specs. Only thin I am thinking is that I have a socket stuck behind the vinyl plastics

That, or the spring decompresses when i hit a small bump and makes the spring rattle in the strut assembly.

Edit: I get a rattling sound in the rear when I hit small bumps and also like threads going up and down the strut tower. Strut is flush with chassis/strut tower, bolts are tight, strut top hat nut is tight. Not sure