Pad rattle is not uncommon for aftermarket pads from my experience. I have gone to using 3M 468 high temp adhesive on the back of the front pads I sell with my rotors to deal with the noise. It's just enough to help the backing plate stick to the piston so they don't rattle around in the caliper. I have sets in stock if you want some, $8 for (4) mailed to you.
2006 Elise with BOE 400 supercharger and some aero mods, CRF floating oversized rotors, MCS single adjust coil overs, CRF exhaust, CRF sway bar w/adjustable link, mono-ball pivots, machined steer arms, baffled oil pan, CRF titanium toe link brace, hardened motor mounts, Ethos wheels w/Yoko slicks