This is according to a report from Motherboard (via Cult of Mac) in which they have been hearing such reports from repair centers. The problem which users are encountering is when their phones start to freeze, and can eventually get to the point where the phone is unable to power on and gets stuck on the Apple logo when booting up.
This is actually not the first iPhone to encounter this problem as Motherboard notes that iPhone 6 and 6 Plus units also experienced the issue a couple of years ago. Apple has since responded to the report in a statement that reads, “We are looking into a very small number of reports affecting the microphone on iPhone 7, if a customer has a question about their device they can contact AppleCare.”
It is unclear as to what might have caused the issue, but some repair shops have chalked it up to phones getting dropped from time to time, while others suspect that it could be because over time, the phones start to bend with use and could cause hardware issues leading to this “loop disease”. The good news is that this problem seems to be relatively easy to fix and typically costs between $100-$150.