Cannondale has determined that the creak from my Rush is in fact a manufacturing defect in the "hotbox" after all. They have placed an order for a white swing arm to be sent to my local dealer and then I'll do the swap and get it all sorted. Seems that all the components for the swing arm are tabbed and slotted and 'pre-assembled' in an alignment jig prior to welding, and that the welds on some of the arms aren't deep enough to tie in the slot/tab juncture. As a result, the juncture makes a creak when loaded laterally. Hell, my Rush would creak just sitting by itself alone in the dark chained to a wall! I could hear it in my sleep!!
Say what you want. Make all the 'creak' jokes you want. I don't care. Cannondale has always, in my experience, done a wonderful job supporting their bikes after the sale. Thanks Cannondale for doing the right thing!
Faulty swing arm...that would explain why I was pulling (whats left of) my hair out trying to find the creak!