[Samsung Galaxy S7 (Exynos) ROMs, Kernels, Recoveri] Nilociety:
Okay, it's been a while but I've come back with an update on the whole microphone issue, and the echo problem.

Just a disclaimer that I have switched from this rom to FloydQ, so there is a chance that any suggestions I make may or may not work for you.

I wanted to share regardless, because no matter what ROM I switched to, this was an issue. I hope that this may assist certain people because it appears that only a select amount of people can fix the issue, or even have it at all.

So it all began with finding an older S5 of mine. I have a habit with turning on the battery saver the quickest chance I get, that includes after I install it for the first time. (we're all aware that older batteries that these phones house are not the best nowadays)

I installed a newer version of lineage on the S5. I noticed the minute I toggled the battery saver on that, it performed a ton worse. The whole reason I wanted to use it was because I wanted to see if it had the same issue as my current S7.

When I turned off the phone with the battery saver on, my friend said that he heard his voice for a split second. The echo issue persisted. With this information in mind, I decided to call myself using the S5 and my daily driver S7 to see if I could figure out what the cause was.

I noticed that switching on the battery saver and off gave different results:

Battery Saver ON: The interlocutor can hear themselves if the application is not focused. This only occurs SOMETIMES while the application is focused. Any sounds that emit from the phone like notification sounds, etc. will go through to the interlocutors end.

Battery Saver OFF: The interlocutor cannot hear themselves regardless if the screen is off, or the application is not currently focused. Sounds that emit from the phone such as notifications, system sounds, etc. Do not seem to relay to the other end.

I have a theory as to how this might be occurring, and may or may not be the answer. I believe the stock rom has precautions in place to ensure the battery saver does not hinder the quality of the microphone, and to not hinder other calling quality related settings. The manufacturer (Samsung) knows their phones best, and their capabilities, so they likely knew this was an issue and patched something with their stock rom to ensure this was never an issue. (Why else would they place the speaker on the bottom with the microphone right beside it?)

Again, this might not work for everyone, but it seemed to fix the issue for me. Make sure to turn off the battery saver when you're calling people. It should also be stated that the android version you're running might affect the way this solves the issue. Different versions come with more, or less levels of battery saving techniques, and may affect your results. If your phone has a battery saver slider (lets you fine tune the level of battery saving), it may or may not be a variable. My S5 running 19.1 had this very slider, and I maxed it out, which seemed to solve the issue on there. My S7 is running FloydQ as I stated before, so toggling off the battery saver appeared to fix it for me.

Hope this helps everyone, and thanks Ivan Meler once again for allowing me to experience the fluidness of your roms!!