I remember reading something about the 71-72 RR/Sats having a resonance problem related to the floorboards. The article showed a weight attached to the floor to change the resonant frequency of the floor and reduce/eliminate the problem. Not sure about where to look for info on that article, but I'm pretty sure it was a Mopar Action article - deep tech, not just the garden variety. Mabye part of their Bold Beeper project?

Clair