Turning off Ok Google probably did the trick. You can still use it when you open the Google app and say Ok Google. The Voice Enhancement is meh in my opinion. It does helps on voice calls but it doesn't turn on when in speaker or bluetooth mode so it's only effective when the phone is to your ear.
First I will say there could be hundreds of variables on a phone, installed apps, root or unrooted, settings, etc. For me my situation started 3 days ago, nobody could hear me. Everyone said my voice was so faint and I sounded like I was in a hole. That was using the speaker or non-speaker. For one day it worked fine in my car connected to Bluetooth but even that stopped. Nobody could hear me. I did some research and cleared cache, took the case off and blew air in the mic, to no avail. I then found thought I would try to use my voice recorder app to see if it was a mic issue. I could not record, I got an error message,
Cannot start voice recording while other application is using audio
But I did not any another app using audio so I found this page:
I followed these steps and all is fine. I sure did open Ok Google to work form all windows in the last release.
Problems due to OK Google enable in all screen. To fix this, find the Google folder in apps, tap on Google settings, tap on Voice, then "Ok Google" Detection, uncheck the option From any screen, and make sure to check From Google Search app, if you still want to use Ok Google from Google app screen. Problems will be solved....
The problem is there are so many apps that use and interact with the mic and that can impact voice calls. Hope this helps.
I had the same problem for a couple weeks. It was the O.K. Google Voice detection. You can turn it off under google settings.