Hey, I thought this was a 'review only' forum?
Ok, I don't know if it's my cat, or not, that causes the rattling. I went under my car three times to tighten some things up I didn't do before, and it could be vibrations from the air pulses that are causing the hooks to vibrate against the header. I don't think the aluminum is that thick and being aluminum, it'd be a total guess for me to try to figure it out. What I plan to do is have the shop cut off the cat and weld on flanges at the cut. That way I can Jet Hot coat the whole header (inside + out) and see if there are loose debris inside the cat that came with the MRT system. I can replace the cat if necessary with any universal high flow cat (and there's a lot out there). But this will happen in the summer when I can take a bike to work instead and set my car out for a few days until I get the header back from Jet Hot. Dreaming and planning sux.