iPhone home button making sound iPhone 4S

Yes, the sound is meant to be audible. I can hear the clicking sound on all of my devices, from iPod touch to iPad3.

Even when the sound is pretty loud??

Did you compare it to other devices? You can also visit an Apple Store again, to let them have a look at yor phone, if the sound is louder than other devices.

I've got an Apple iPad also. When I push the home button, I can hear the clicking sound. But it is hard to hear it, it's much easier to hear the sound on my iPhone 4S.

I'm in Holland... We have only one Apple Store in Amsterdam. And I'm not close to Amsterdam. Do you think de Apple Premium Reseller can help me?

Yes, at least you can try another iPhone to compare. Maybe your Apple Premium Reseller can also help you to get it serviced by Apple, you're still under warranty.