Desktop/hard drive making whistling noise from power supply

[BinkerNate]

So I have an iBOYPOWER desktop. Recently it was making noise at startup that would go away after a couple minutes. The noise can be described as a whistle. Last night, it was making the noise all night and it was decided to take it out and clean the interior. Did so, alot of dust, but it was fine like normal.

Now to do this, we had to unplug everything as you should, and switch off the computer from the back.

When we put it back together, we switched the power on from the back and all of a sudden it makes a high pitch whine/whistle. Of course, not the case when off, but when I turned on my computer, everything was fine.
I did research and we got many extremes: its fine and it'll go away or be normal over time, its not fine because the CPU might be hurt or the power supply might be dying, etc. So far, even with last night on the mind, nothing bad has happened (yet). And I really don't know what to do. I'm afraid of this thing making that noise once I shut it down for the night.

Any ideas or advice?

Additional details: got this back in 2014, high quality, custom, no problems whatsoever until now.