I had those same test pipes. They are JUNK. Same problem that you mentioned. The flex joint in the test pipe went to $hit and made the rest of the exhaust wiggle around whilst driving and hitting the w brace under the mid pipe. Bought ART pipes and the problem went away lol :) hope this helps

Thank you all for your input. The problem was found.

It would be helpful for others if you could describe what was found.

I was going to add, I have the same Z1 Cold Air Intakes and found mine were occasionally vibrating off the strut towers.

I'm interested as well to see what it was.

:iagree::iagree:

heat shield above the X pipe had a crack. It was welded and problem solved!