"What the hell is that noise??"
In my own work with DC-DC converters, I've come across several situations that can make them whine. From an engineering standpoint, it can actually be quite involved to make a converter quiet under all possible conditions.
DC-DC converters are naturally unstable so it's not a trivial matter to perfectly stabilize one of any type. It's because control has to compensate for the natural instability of the circuit and that can be a complicated thing. The goal is to make the converter "unconditionally stable".
A converter can be stable under some conditions and unstable under other conditions. For example, under various input voltages and output currents. When you run into an unstable condition, the converter may whine and voltage may fall off, but not necessarily. It's because the converter's controller is taking duty cycle from tap to tap in its failure to properly control the output. That can happen at a frequency in the audible range which results in a whining noise.
Another thing that can make a converter whine is when it hits current limiting (as determined by the controller chip). Typically, the converter resets and restarts in this case. If the converter is reseting and restarting at a rate in the audible range, it makes noise.
A converter may whine if it drops in and out of continuous and discontinuous conduction mode. That happens at the transition point between heavy and light load which is dependant on design. If the converter transitions back and forth at an audible frequency, again, you can hear a noise.
A cheap inductor can resonate in the audible range even under ideal conditions due to alternating magnetic forces on the inductor core imposed by the switching frequency and ouput load. A good converter uses the encapsulated/shielded type of inductor that is not prone to audible resonance. Those are the square solid looking inductors you see on the OKR-T and TI switching modules.
In general, DC-DC converters can be noisy things and it takes some highly detailed engineering to make them quiet under all conditions. I wouldn't expect perfection from an inexpensive converter module designed in China and purchased off eBay. You'll probably have to live with some noise or upgrade to a higher quality part like one of the Murata or TI modules.
yeah 
I doubt very much that I'll ever even come close to the finesse at modding that you have shown. 
, I'm pretty sure it is ... 
all!
