The problem with this thread is that it actually discusses two issues that probably are somewhat related. The first one (and also the one that the name of this thread hints about) is about the buzzing, hissing, chirps etc that comes from the back of the phone. The other issue is that some people can hear the same or similar sounds when they listen to a HD (4K?) video recording they made with their phone.
It's not always easy to understand when reading peoples post which of these problems they have, the first one, second one or maybe both?
Also, people should stop using the word "normal" in this discussion. If almost every new iPhone 7(+) has this issue it must be considered as normal, whether you like it or not. Sadly it is normal for this phone at this certain time. It may change over time, Apple may redesign and do running changes, no one knows...
Many people also compare against their old iPhones. My personal oppinion is that you can't actually compare against the 6, 6S etc. The only thing the 7 has in common with those older models is the look and the brand name. The 7s has a new internal design, new processor (that is MUCH faster than the previous one), new hardware etc. I think you are comparing apples(!) and pears...