Hi Arthur,
Thank you for your advice! Of course, your statement makes sense, but I don't need a truly scientific test and real precise numbers. I trust my ears. I work in the audio business for 20 years now. A also have regular measurements of my hearing. That's required for my job.
And it's not important to me how much louder the sound really is. The fact that it is louder and different is enough for me.
Meanwhile it's also confirmed by ohter X-H1 users, that the shutter sound in portrait mode is different/louder. I will also visit my favorite camera store to make a final comparison with another X-H1 on Thursday. But so far it seems that my shutter is ok, and this is a "normal" behavior. And that's ok for me! It's a great camera!
I'll keep you updated...