Here's a video of the sounds coming from the computer, it is very faint, comes in peaks, and sounds almost like a fan is hitting something. My speculations is that the power supply fan is dying, and since the power supply is now about 6 to 7 years old; this is a good guess.
I am looking to replace the power supply, but not in anytime soon. The power supply is never drawing more than 400 of its stated 850w output.
please got to pcpartpicker.com and assemble your rig and post the perma-link /// so we have a better understanding of what we are looking at in a uniform format.
Just stop each fan briefly and check/replace the one that makes those sounds. If you want to replace the psu a xfx 550w or something like that should be adequate and not too expensive.