Had to change this response. Only use a stress ball. The Hulk was too small and didn't fit tight enough so it got rolled up in the shade and was a bear to get out.
I just jammed it between the bar and the roof right in the middle. The clip trick that everyone uses just adds pressure to the bar on the passenger side which can also prevent the rattle but mine kept coming back. Putting more pressure in the middle of the bar seems like a better solution and the foam keeps the pressure on the bar despite temperature changes.
So my felt pad under the clip only works for so long but the rattle eventually comes back. I finally came up with a permanent solution!!! The black cross bar that the sunshade rolls under was always the main suspect in my mind. Just for the heck of it I jammed a microfiber towel between that bar and the roof and the ticking/rattle never came back. A foam stress ball works even better and allows the sunshade to operate just fine.
Could be the AC system. I used a can of AC system cleaner after my drain tube became clogged. You just shoot it up the drain hose and let it sit for about 20 minutes before letting it drain out.
I've always just done a radiator drain and refill every 3rd oil change. Motorcraft yellow concentrate is pretty cheap and the 3.5's internal water pump bearing issue always frightened me. My 2011 SEL 3.5 just hit 160,000 with no issues.