The sound, described by some as a hiss or screech, has drawn comparisons to how a computer’s CPU/fan can begin to whirr when pushed to the edge. Basically, if the smartphone is working overtime by, for example, running lots of applications at once, it begins to make a faint hissing sound. The noise was first pointed out by Stephen Hackett at 512 Pixels and was quickly followed by other users reporting the same problem, including TechCrunch writer Darrell Etherington, who noticed the hiss while his iPhone 7 Plus was going through the setup process.
— Darrell Etherington (@etherington) September 17, 2016 Hackett uploaded a video to YouTube with a recording of the sound (below):
Hackett noticed that the sound, which was “loud enough to be heard even if the iPhone is just sitting on the desk,” was worst when the iPhone performed processor-heavy tasks. For the moment, Apple customers and technologists have been debating the exact cause of the curious hissing sound. “Some suspect coil whine or similar electromagnetic effects, but there’s no guarantee that this is the case,” claimed Jon Fingas from Engadget. However, the issue doesn’t appear for everyone. Several customers reported that they put their iPhone 7 under enormous stress but heard no hissing sound at all, leading some to speculate the problem could be a manufacturing problem rather than an in-built design quirk. Marco Arment, Tumblr co-founder and iOS developer posted his own explanation to Twitter saying the noise may be happening for a “good reason, but it’s still unfortunate and ungraceful”. “It’s the phone equivalent of hearing the fans spin up loudly whenever your Mac’s CPU gets used to its actual potential,” he wrote. Since, the iPhone 7 was produced with the hugely powerful A10 chip that outpaces its predecessors and Android rivals, it is possible that it only emerges when the device is under heavy load and emanates from the general area where the processor lives. While Apple has not yet made any public statement or recall regarding the abnormal hissing sound, but it did offer to replace the smartphone of Hackett, who pointed it out first.
