Same problem here, that's how I found you guys.
First I thought the ratlle also to be from the b-pillar. But removing the interior cladding proved to be a bit difficult. I was afraid for applying too much force and breaking something.
After a couple of weeks with the weather going colder and dryer, I was driving around with the rattle as usual and started pressing gainst the window. All of a sudden, the rattle was gone.
Now I have been researching this site, and found arek_4k's post. I investigated and it seems like a good possibility for me. Today I went and taped the area with some painters tape to see if the noise would stop. When standing outside and pressing on top corner of the door, the noise didn't stop, but while driving the car, I couldn't hear anything.
But I must confess, while investigating the area I was pushing the rubber seal quite a lot (the one in the picture above within the red circle) making the seal less 'stiff' and warmer than usual.
So when I removed the tape, there was also no noise to be heard while driving.
I then went and washed the car, and the noise you hear when pusing on the door standing on the outside was also not there.
So I now have some painters tape in my glove box and a kitchen sponge which I could insert into that cavity of the seal. But my best guess to definitly locate where the noise is coming from, is to ride around as usual and upon hearing the noise, make the rubber on the top corner wet and warm and see if the rattle is still there. I assume that the cold and the resulting stiffness of the rubber is causing this problem. Not sure if unserting a sponge is going to solve it, but I first want to make sure this is the cause.
The material from which this part is made is different than the other seal araundthe window and door. Even when it is cold, the other seals are still very flexible and soft.
I'll let you know when I find something.