Affects all iPhones out of the box, no apps installed or anything setup like Siri etc, basic scratch setup, crackles on calls. More noticeable when the volume is at max. 16/16 handsets at our office have the bug, all from different suppliers and on various networks.
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audio driver for earpiece. As its only affects calls (cellular, VoIP and Wifi calling) and doesn't affect media playback.
This actually makes me feel better about it getting a quick fix. If it truly affects all (or a large number) of phones they can't ignore it and will do everything they can to fix it without replacing hardware.