I agree the power supply, even if its an underrated low wattage power supply, is the last thing I would suspect.
 

Well guys, the success story: Swapped out the motherboard (Asus Z170-AR) with a RoG Maximus Ranger VIII. No more crackles. 

The OP's issue reminds me of my setup a long time ago. Some of you may recall my entire, wind-bag thread about a very similar issue: http://forum.cakewalk.com/Sound-Crackling-CPU-Latencies-When-MultiDock-Maximized-m2921285.aspx
 
If you can't seem to fix the latencies, no matter what you do, I suggest ditching the nVidia card and going ATI/AMD, or get a new motherboard.
 
It seriously sucks, but audio quality is NOT a concern with any motherboard or graphics card manufacturer. nVidia is the worst, in my opinion. The card, a GTX670 at the time, did NOT play nice with a particular motherboard, no matter what I did. To make it work, I ended up hacking the registry to force the graphics card to operate at 100% all the time.
 
And just to double-check, the power options in Windows for CPU speed is set to 100% max and 100% min, correct?

The ASUS "ROG" (gamer) motherboards do favor audio with improved chips, caps, etc.   But as Windows, even in Windows 10, treats audio as a lower priority function Windows needs to improve audio support functions.  The sound device is always placed on a shared Interrupt with a higher priority device.  

fireberd
The ASUS "ROG" (gamer) motherboards do favor audio with improved chips, caps, etc.

 
True dat! ASUS was the maker of the board I went with prior to my current build. The ASUS board had benchmark data proving it was inherently low in latencies.