It's definitely something that a foldable user will not see the more you use it, there are a few of us over here that have been using them for a while so we are definitely in the category haha. I always get insurance on my foldables so I highly recommend that, I have one case that has the noise that makes it seem like it's the hinge, by chance does your brother have a case that has hinge protection? Because usually you those are the ones that make a little noise opening and closing as well as make the phone seem thicker.
For those first time buyers with the upcoming iPhone Ultra fold I recommend watching Jerry's video, these phones will surprise you with durability.