Loud squeaky door/vent opening noise at startup

There is a lot of threads on different noises but seems nothing on this particular problem – after four months of driving (appx 1000 miles) my Prius started making a loud squeaky door/vent opening noise at the startup somewhere from the back of the rear passenger seat. The noise is quite loud and lasts for about two seconds. It happens only when it is hot outside and when the car was standing under the sun for a few hours. The noise happens at the same time as the usual double-click noise also from the back of the car. There is no squeaky noise when the weather is cold (only the usual double-click). The car seems to be running as usual, but I am sure I have not heard this noise at startup before even on the hottest day. I should probably take it to the dealer, although it’s getting colder up here in Canada and the service might not detect anything. So, I wanted to check with you guys, has anybody had similar problem?

 

I've read other threads about the double click. Apparently, many other users can hear it. So, I am not too concerned about it. By the way, my hatch floor is half open because of the umbrella stroller that I put under it, so maybe it contributes to it. Anyways, the weather is getting slightly colder and the squeaky noise has gone. So, I think I should be fine for now. Strange that nobody else had the same problem though. There is a lot of Prius owners that live in south and I was hoping that somebody has experienced the same problem.