Hey Xer,
I totally forgot I had a WLAN-Card. It is a TP-Link: TL-WN951N. I just updated the driver to the newest version, I got it from here:
Select Qualcomm Atheros wireless driver
It's working fine. However, I'm not using WLAN anymore, so I should just remove it from my board.. maybe another day. Thank you for pointing me in the right direction!
Fingers crossed for the second BSOD!!