Hello my problem is a bit weird one. I have a PC and Nintendo Switch. I want to hear both devices at the same time as I talk on teamspeak with friends and play either PC or Switch games. So I bought Behringer 802 mixer and some 3.5mm to dual 6.5mm jack cables. Plugged one cable to my green sound jack in my motherboard and dual 6.5mm to the mixer and everything is fine. Connected my Switch to a monitor via HDMI and plugged a cable to monitors headphone jack and dual 6.5mm to another input on the mixer. I hear sounds now the problem is there's buzzing sound and when I regulate volume knobs the buzzing either strengthens or gets weaker. There is no issues on both input channels using separately with either PC or Switch. As an output I just use my Sennheiser HD598. What can I do? How do I eliminate the buzzing? What may be the problem? There's also a lot of electrical cables around. Thanks in advance.