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An Applied Investigation Into Graphics Card Coil Whine
jones_supa writes We all are aware of various chirping and whining sounds that electronics can produce. Modern graphics cards often suffer from these kind of problems in form of coil whine. But how widespread is it really? Hardware Canucks put 50 new graphics cards side-by-side to compare them solely from the perspective of subjective acoustic disturbance. NVIDIA's reference platforms tended to be quite well behaved, just like their board partners' custom designs. The same can't be said about AMD since their reference R9 290X and R9 290 should be avoided if you're at all concerned about squealing or any other odd noise a GPU can make. However the custom Radeon-branded SKUs should usually be a safe choice. While the amount and intensity of coil whine largely seems to boil down to luck of the draw, at least most board partners are quite friendly regarding their return policies concerning it.
My anecdotal experience is that sometimes it's a ceramic diode getting hammered by out-of-spec back-voltage and ready to explode, and sometimes it does explode spraying ceramic shards all over the electronics lab. Root causes may include a dodgy transformer (pulled out of an old Hammond organ) with a highly questionable output waveform because you're a broke undergrad and it was cheaper than buying a new one.
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Full disclosure: I worked on this *exact* issue at NVIDIA for a brief period, although several generations ago. Usual disclosure applies - the below is my opinion, not theirs.
It doesn't surprise me that the NVIDIA reference cards do pretty well; they took the issue as seriously as some of their customers do. We made some fancy measurements to evaluate different methods of reducing the noise; indeed, some of the "common sense" things a designer can do are actually wrong. For example, #1 from the parent (fill the inductor package with something to keep the coil from moving) isn't necessarily a good idea. In some cases, that actually makes the vibration *worse*; rather than prevent the coil from moving, it helps transmit the motion of the coil to the PCB, which can then act like a sound board, making the tiny coil's vibration into something audible. (The sound board is the part of a musical instrument that is forced by the string to vibrate, making sound. It's what makes an acoustic guitar make noise when a string is plucked, while an electric guitar is relatively silent with no amp.)
That's not to say that encapsulation is a bad idea necessarily - just that this is a much more difficult problem to solve than you might imagine at first glance. And something that works well for a particular application/GPU/inductor/card combination might not work as well for a different combination.
A long time ago, I had a PowerBook G4 that had a buzzy whining that I later (while working on this problem) learned was from the inductors. I discovered that by using the CHUD Tools part of Apple's developer tools to disable the "Nap" option (this is the CPU Nap power-saving mode, not the much more recent "Power Nap" marketing-branded feature), the whining would go away, because the current in the inductors was much closer to constant.