2008 E-350 shaking and suspension noise
 

I've got a 2008 Ford e-350 12 passenger XLT van with 74,000 miles. On a trip up to LA with six passengers, on a pretty badly washboarded section of the 405, it started shaking with the rough pavement at 70+mph. Slowing down to 60-65 stopped the shaking. Once I returned to smooth pavement I had no problems up to 75mph again. I don't think I've ever been on such a bad piece of interstate, so it could be that this is normal behavior for the van. Regardless, it seems to have shaken something loose:

Coming into town over a low-speed bumpy road I'm getting fairly loud crashing/banging noises - it sounds like it's coming from the rear suspension. I put new shocks on the vehicle 10,000 miles ago. Any ideas as to what I should look for? I have a long trip planned for next weekend with 10 people, so I'd like to get it fixed soon. Thanks!