IPhone 7 Audio problem with calls

Since last week my wife's IPhone 7 has no audio on calls. I have done all the checks and tests and have read although there has been a known problem with audio ic failure, I now suspect the issue may be something else. Co-incidently, I have an Iphone 7 too and it now has the same issue, although intermittent, since a few days ago. I mentioned this to a friend who had trouble calling me, and he told me his wife has the same problem with her Iphone 7 in the past few days. I see Apple no longer repairs this out of warranty issue, so before I go and spend money on an audio ic repair, (that may not fix the problem) I wondered if there are any other solutions, and welcome any comments on the cause of the problem.