I'm curious as well. The only thing I can reason is that the springs or the way the springs are installed might be sending vibrations throughout the car, and that it just happens to strike that magic frequency causing the rattle.
In some ways, I can see the correlation. I've found that it happens only certain times over certain road conditions. It's nothing structural -- just annoying at times.
Richard | GapBoyPCS
The odometer just keeps whizzin' by...