Business Insider
People started reporting as early as September 22, the day the iPhone 8 and 8 Plus went on sale, that they experienced crackling audio issues during regular phone calls and Facetime calls while using their new iPhone's earpiece.
Apparently, the issue was sporadic, with one online commenter saying it happens on one out of every three calls.
It's not unusual for new Apple products to come with a few bugs at the time of their release. For example, the new Apple Watch 3 with LTE has a glitch that reduces the Watch's LTE performance. Apple has also acknowledged this issue, and said it's working on a fix.
Ideally, newly released products shouldn't come with any bugs or glitches, but the reality is that they're pretty common. They shouldn't pose much of a problem as long as companies acknowledge them and provide updates containing fixes.
To update to the latest version of iOS11 and get the fix, go to Settings > General > Software Update > and tap Download and Install.