I believe I've fixed the rattle in my 22 MYP. I used this tool to pry off the lower mirror cover, but any plastic pry tool should work if its thin and strong enough. I just worked it around the until I could hear the clips pop then you can basically pull it straight down and remove.
Then I removed the mirror with a T20 torx driver. The manual says you need a security T20, but you don't, there is no center "nub" on the screw itself preventing using a normal T20 torx bit. I found it easier to unclip the wire in the back once the mirror was free and I could turn it around.
With mirror out of the way, you just need to use a pry tool to free the upper housing front two clips. They pop off pretty easily. I originally removed the entire upper housing, but that is not necessary. Getting the housing free from the head liner was the toughest part, so I recommend you don't even bother.
You just need to free it enough like the next pic shows to install some rubber feet. What I found when I removed the entire upper housing was if I tapped on the triple camera hood (thats the part the upper housing covers), it sounded very similar to when I hear the rattle or buzzing going over rough roads. Like it was vibrating against the windshield or the upper housing cover. Because of this I thought if I could add some rubber feet to the bottom of this cover, with everything back in place, it would be more securely held against either the windshield or the upper housing cover. The arrow shows where I installed the rubber feet. One on each side and one in the center.
Here is a pic of the rubber feet I had laying around. I believe they are about 1/8th inch thick.
Here is a pic of what it looks like with the rubber feet installed.
I then put the upper housing cover back in place, clips right in, and went for a drive before I put the mirror and lower cover back on. I used a section of rough rode that I could always reproduce the rattle and to my hearts content...silence.
This is a pretty easy fix as the only wire you need to disconnect is the mirror and you don't need to remove the entire upper cover, just lower it enough to install the rubber feet. I'll report back if there is any regression, but I think I may have found this rattle. Fingers crossed.