Constant Buzz sound from Speakers

May 6, 2018
I have three devices. A computer, a PS4 Pro, and my Z623 Logitech speakers.

When I connect either the PS4 OR the computer to the speakers, the speakers operate as expected without a constant buzz sound.

When I connect BOTH the PS4 AND the computer to the speakers, a low (frequency AND volume) constant buzz sound begins.

Neither of these situations cause issues with the quality of sound coming from the speakers. It still sounds great. Thus, I attribute this to power consumption but I need to know a few things.

1. Why is this happening if there exists multiple ports to plug in multiple devices?
2. How do I avoid this without having to repeatedly unplug and plug devices causing material degradation of the ports?
3. If I keep both plugged in and let the buzz sound continue, will it cause a problem in the future that I should know (Damage to any device, risk of blowing up my electrical outlet)?