WD15 dock with DELL XPS15 causes static in speakers after using headset

I've got a WD15 hooked up to my XPS15 laptop and it works fine. Latest drivers and chipset/BIOS installed on both Dock and laptop.

I have a pair of external active studio speakers hooked up to the 3.5 mm Speaker out jack on the back of the dock and it works fine.

However if I use Google Hangouts or Skype for business calls and plug in a headset to the front 3.5 mm Headset Jack of the dock the external speakers starts a high pitch static noise. If I then un-plug and replug the 3.5 mm jack for the speakers the noise is gone. The sound and mic of the headset is working fine from start.

The same thing happens when I unplug the headset from the front of the dock, the external speakers starts to "hum" static noise. Again un-plugging the 3.5 mm jack of the speakers and plugging it in again stops the humming static.

If I instead plug the headset into the Laptop there is no problem and the external speakers remains quite.

Why is it doing this and how can I get rid of this annoying behavior?