Seven days? Either return for exchange or try this
So there isn't actually anything wrong with your MixAmp Pro TR and this problem doesn't affect majority of users although we do see it. What causes the problem can be many things but it's generally a ground loop problem because your MixAmp Pro TR is being powered by a separate source other than your PC and this causes a buzzing to be heard. The reason it's not heard through your headset or if you was to connect your headset to the stream port is because the headset isn't self powered and doesn't have a separate ground. There are a few ways to remove it such as placing a 3.5mm Ground Loop Isolator in between your stream output and the 3.5mm to 3.5mm stereo cable or using a cable that spoonhandle manufacturers.