Haven't had to track down a rattle...yet...but I've got a few ideas.
When you say spindle housing, are you referring to the frame side spindle housing with the brass bushings? There should only be the one washer on the bottom followed by the bolt which gets tightened to about 40-50ft/lbs.
In terms of the washer stack on the adjustment buckle, I have 5 washers under the joint and 4 above.
Have you looked at your turnbuckle adjustment? The horizontal carrier tube should begin making contact with the saddle block about 4-6" prior to the tailgate reaching fully closed. The last couple of inches of closing movement should have a bit of resistance as the tube "seats" into the block.
Also, check the alignment of the saddle block vertically as compared to the horizontal spindle tube. I like to run the centerline of the block just slightly (1/16-1/8") above the centerline of the tube. Since I'm running 37s on slabs, there is just a bit of droop in the carrier due to the heavy weight of that combo. Having the block slightly high allows the spindle to get "picked up" by the saddle block.
Hopefully this helps and I can easily snap a few pictures if that would be helpful.