Floating disc rattle?

Thanks for your comment. My disc set up has no wavy washers, so the disc is free to rattle sideways - so that's something I will explore. Because my bobbins appear tight in the aluminium carrier and slack in the disc, I now suspect that the braking force has tended to drag the disc into the carrier, (stainless v aluminium) so all the tolerance is now on the disc side? Today I will attempt to (gently) dislodge the bobbins from the carrier - and also look at the availability of wavy washers.

The disc set up has been on the bike a long time, but not done a high mileage - and neither has it been used heavily. The fact that corrosion will occur between stainless and aluminium leads me to suspect that as the likely cause. So maybe I need to repair or replace the aluminium carrier rather than the disc?

Although my RGM disc does not have wavy washers it does have wavy C clips, which hopefully you can see in the photo? There isn't room to fit wavy or Belleville washers as the C clip is still required and the other washers wouldn't fit under them. The problem appears to be that although the wavy C clip is pretty well tight up to the aluminium rotor base, it is a full 15 thou shy of the disc at best, that is to say when the closed part of the C clip is over the disc, and the disc is pushed away from the clip. When the opening in the C clip is over the disc there is even less restraint provided to lateral movement of the disc.
In hindsight this was probably not the best engineering solution - or if it was - it should be lifed with some kind of check criteria applied when too much play develops? It doesn't seem as though the problem might be solved with a new set of buttons and clips - although a comprehensive strip down and measuring session of all of the parts might show otherwise? ? 

The question remains - how much is too much rattle?