So I'm not really sure what the phenomenon is.. but I can only describe it as resonance. Here's what happens:

I'm coming downhill in the same gear, and due to the acceleration, I have to change to a smaller gear so as to keep pedaling. Even after I change one or two gears, I still have pretty high cadence, and if I try to maintain this cadence, the bike starts bouncing very noticeably. But then if I change to a smaller gear, the cadence reduces a bit, and the pedaling load becomes large enough that the bike doesn't "bounce" anymore.

Has anyone else experienced this? Is this regular bike physics, or is it only in Ti frames, or only in Seven frames, or only on my bike? Is there something I need to change?

Thanks!