Mac Mini (A1) Fading Sound

When using a headphone jack via my Mac mini w/ A1, there is a tone that fades in and out frequently similar to the ringing you'd hear through a short bout of tinnitus. It's subtle, but If I'm not listening to anything it is not only annoying but very noticeable.

I have not tried bluetooth, but every device I've used through the rear headphone jack (different cables included) has resulted in this pulsating fade in-out tone. I've also used different power cables and outlets in case it was an issue in power draw, but no difference.

What's interesting is that when I play a video, I hear a feint popping noise as the video/music takes over and the sound goes away. Stop the audio however, wait five or so seconds, and it's back to the same annoying repetitive fade in-out tone. I'm wondering If anyone has had the same issue, I'm leaning towards it being due to some form of interference or some sub-power cycle the Mac mini uses.