Raspberry Pi 2 - Airplay Problems

Hi everyone.

I’m running Volumio 1.55 on a Raspberry Pi 2

So far it works fine. I’m still testing and therefore using the onboard sound plug of the Raspberry Pi.
This works fine when I play Mp3 Files form a USB drive.

When using Airplay the sound volume is much lower (too low for my purposes) and I can hear quite some noise.
It’s the same Problem from different Airplay sources (MacBook with iTunes, iPhone, iPad) and doesn’t change if I change the volume.

any suggestions?