Today Apple released the iOS 11.0.2 update for iPhone, iPad, and iPod Touch, just two weeks after the initial release of iOS 11. This update takes care of a few specific problems, and may take care of other issues as well. Of note is a fix for those with iPhone 8 and iPhone 8 Plus that have had a problem with crackling while on a call.
You can install the update in the Settings app > General > Software Update.