Our first attempt to solve the problem was using some egg create foam between the headboard and the wall, but a good jostle would allow it to hit the floor and resume making noise mid jostling-not an effective solution. It also wasn't the most attractive or subtle solution.
The long term fix? Read on...
Step 1: Supplies and Tools
Tools-unfortunately this list is incredibly short, as I usually am all about my tools. But, this is simple and straightforward.
-Utility knife/craft knife/etc
-Hot glue gun
-Ruler if you really feel inspired to draw straight lines
One of these will work for a queen size bed and should work for a king as well. If you have a California king, you may need to make two.
Step 2: Cut Away
Based on the thickness you need you may have to adjust how many of the small block pieces you will need. You will need two stacks that stack up to the thickness required-there will be one base and then stack as many on top of that as you need, which will depend on the thickness of your foam.
When you have your layout with enough pieces, cut away!
Step 3: Assembly
Your pieces will be assembled as shown.
-The two large rectangles should be hot glued to the flats you cut on the bottom of the upside down U. This is to position your pad high enough to work right.
-Glue your smaller rectangles onto the top, outer corners of the upside down U, stacked up to achieve the thickness you need.
You may notice that there are reinforcements on the joint where the legs meet the U-these are probably not at all necessary and I put them on as a precautionary measure. They really shouldn't be necessary and if you are running close on foam, skip them for sure. There isn't much vertical loading on this at all.
Step 4: Place and Test! Shhh...
The floor mat foam will allow for some compression to cushion for movement and allow the headboard some flex, but will be firm enough to silence the headboard from its normal wiggles. If the headboard still manages to thump the wall, you need to add another piece of the small rectangular foam to the stack. Jostle as necessary to test. Rinse lather repeat as necessary to get your foam thickness right. When you get it right...