Steve,
I think we are talking about two different conditions. You describe a intermitant sound frequency condition... a vibration that occurs at a given range of vibration frequency.
My condition is a drone that increase in intensity (not pitch) as the motor increases in RPMs. An improved resonator system would probably help eliminate the drone sound but since that is not possible it appears that my only alternative is to better sound insulate the trunk area... a section that has hardly any insulation. In fact the trunk seems to magnify the sound something like the housing of a kettle drum.
Maybe the car will be nick named the "The Kettle".
