It almost looks like the panel is trying to bow inwards slightly and being stopped by some structure, but I can't really tell from the pictures.

Throwing some ideas out there. This is indeed weird.
Has the door had any excess weight applied to it? Maybe someone fell into it and weakened the skin enough to get it just starting to yield, so that air pressure when driving it causes it to get worse.

OR.... !!!

I think I've got it here, hear me out.

Anyone know how the door skin is kept on the frame? Is it spot welds in the middle, or is it suspended by the exterior structure? Because, if one broke or a few we're not good, the aluminum skin would be free to vibrate at speed. Aluminum has no fatigue limit, meaning that no matter how small the vibration, it will eventually yield. Yielding under load would cause expansion of the panel, thus deforming it. If there's some structural member behind that crease, it would yield around that member under aerodynamic load, and possibly pop back out when there is no load.

This can also happen if the skin were to be too thin, or defective in some other way regardless of the attachment points.

Yeah, I'd put my money on this being water freeze damage.

Anything plugging the drain holes in the bottom of the door?

What are you referring to?

This is more or less what I was thinking when I asked if there were any weird noises or window issues. It isn't aluminum though it is ordinary sheet metal. The only aluminum component is the hood.

I wondered about that but it is pretty high up and I would think ice would cause bulges not a nice straight line.

Not if was pushing something else.

Steel can still yield with cyclic loads though. The skins seem pretty thin.

I like this freezing idea.

OP, does one door feel heavier than the other? Like when you close and open it? Is the car stored outside?

Oh I agree. I didn't separate my statements very well. The aluminum was a side bar not joined to the rest of the statement.
Tried to find a pic of the door structure but can't. The little bit that can be seen does not appear to have any structure there.

True. The ice would partly melt at some point though and should make a hell of a racket when you close the door. Would also jamb the window mech. I am just not seeing it being ice that far up.

Anybody got manual page showing the internals of the door? Can't tell exactly from OP's pic, but some of the heavier structure of the door is in that area.

Window mechanism, maybe, but that would make an obvious noise. Still think water problems is the answer.

OP, if you knock on that bulge, along the bulge, does it have any give or flex at all? Unless you have some sort of alien baby growing in your door, something is or was pressing against the metal. Need to find out what it is!

OP, did you get blasted with a heavy load of snow or ice while driving? Snow plow while parked?

Can't rule ice out of course but it should be obvious if it was in there. There are no other stress indicators that can be seen just that one almost straight line.

Hmm, but ice could freeze first to the inside of the door skin and move inwards, thus pulling/pushing on the skin itself without having causing problems with the windows. I can see that exerting enough force to form a crease.

For clarification I'm talking about mist freezing to the metal.