The sounds in German swingers clubs can be quite revealing. The men tend, for the most part, to be silent, with perhaps a slight grunt at orgasm. The women, slightly more vocal. But other than the stiffled sounds, the Germans I've met in German clubs are quite open. However, this course, is a self-selecting population and certainly not representative of Germans in the wild.
My first sexual encounter with Germans was many years ago when I lived somewhere tropical. A friend of a friend was dating a German tourist. He invited my friend and me to join them one evening, and it was clearly something sexual. She was travelling with another woman so it was 3M and 2F. It started out as separate room fun (MMF in one, MF in the other), but after the we swapped once we all ended up in the same room. So based on that I thought Germans were pretty open. Then I met a German couple a few months later, at their hotel. And he just wanted to watch football while she and I enjoyed each other.
Now that I live in Germany I feel that, in general, the Germans are reserved. I don't think I've hooked up with any Germans outside of online dating and swinging sites. Maybe thats me. But there are some very adventurous German men and women, and perhaps, many more who would love to be adventurous but just need a helping hand.