rrrob

Could be load-pull from the processor causing the "quiet, stable" audio reference ground voltage to fluctuate when the application processor is running at full capacity. Or electrostriction of capacitors causing the logic board to vibrate at an audible frequency. The old RAZR V3's used to have the latter problem with their displays—a perfect combination of display resolution, panel size, lens air gap, and frame refresh rate caused them to resonate at an audible frequency.