Some iPhone 7 and iPhone 7 Plus models apparently make weird noises under heavy load. Early buyers like Stephen Hackett noticed hissing sounds, that seem to originate from the back of the iPhone, apparently where the new quad-core A10 Fusion chip is located. Stephen did record the weird noise and posted it on Youtube (see below). Similar reports are coming in from all over the world, where the iPhone 7 started to ship to customers last weekend.
The hissing sound apparently gets worse under heavy load like when a benchmark is running but some users also report hearing it during installation or when the backup is restoring from the iCloud. Others on the other hand report no such noise. Stephen was able to get a statement from Apple Care who suggested to swap his phone at the nearest Apple store. This however, might prove to be difficult at this time because of limited supply. At the moment it is unclear how many iPhone 7 models are affected, we have not heard an official statement from Apple about this matter yet.