You can get underneath in the crawlspace to install additional support and damping material. You can make the floor more rigid by adding support beams and you can line the surface underneath with a layer of expansion foam. The best thing is to use horizontal beams buttressed with vertical supports extending to the ground. Between the support beams and the insulating foam, you can do a lot to tame the resonance.

The cost of taking these steps isn't too bad if you do it yourself. If the crawlspace is dry and reasonably clean, it isn't too bad either. If you decide to take these steps, please keep us posted on your progress.