My girlfriend has a USB headset, and when we're in a skype call together I can hear this constant hum/beeping noise, here's a quick recording of it: https://www.youtube.com/watch?v=05R7JO9UT10.
We've tried the front usb 3.0 ports, the rear 3.0 ports and rear 2.0 ports, no front 2.0 ports on her...