[Sprint HTC One (M7)] AttackManatee:
Solution - Lower mic replacement

I recently experienced this ongoing problem that started out of the blue one day with one of my Verizon HTC Ones. After reading this and other similar threads, I first tried everything from physical cleaning, to all software solutions including completely reformatting all user partitions, and installing the latest RUU for my model phone. None of this helped. In my case, I could put a piece of tape over the camera mic while cupping my hand around the lower mic during calls as to be somewhat heard. This was problem was slightly different than the OP's post in that mine was occurring 100% of the time during the conversation for all conversations (I was able to verify this by listening to it from my wife's phone), while before this problem occurred the mic wouldn't cut out or remain suppressed at all. Speakerphone was the only other viable solution, but the tape had to be removed as speakerphone uses the camera mic. The odd thing was that most audio and video capturing programs would pick up the each microphone flawlessly. As mentioned in this thread, I figured something was amiss concerning the noise suppression feature of the mics during a phone call. After changing as many software options as I could (including toggling the Noise Suppression and Enhanced Privacy toggles), and ultimately returning to a stock RUU (I'm was S-OFF running PAC-MAN ROM), I decided to try replacing the bottom mic from my previous broken HTC One that I retained for parts.

REPLACING THE BOTTOM MIC SOLVED MY PROBLEM COMPLETELY! :victory:

This may or may not be the solution for everyone, but for those that have this particular issue (it seems from what I remember that there are about 3 similar, but slightly different type scenarios mentioned in this thread), this is what worked for me as there were no working software solutions. As for opening the phone to get to the board, that's another issue all together which requires a couple of thin guitar pics, a hair dryer to loosen the glue (yes, my Verizon version had glue holding the case on, some people report that some HTC One models don't.), and a ton of patience. There are a few YouTube videos on how to do this (some better than others), but for those reading this thread that have the Verizon model (Yes, I know this is the Sprint forum), know that there are a couple of ribbon cables and antennas that attach to the daughter board to be aware of near the volume rocker that isn't in the international phone version displayed in those videos. I had to learn this the hard way, hence why I bought the 2nd phone and have spare parts out of the first. (I was converting the silver phone to a black phone by changing the case and grills from parts ordered online as Verizon never offered the black version.) So being that I've had both phones apart before, it was relatively easy for me to do it again to try to change mics.

I wouldn't recommend this repair for most people, but it might be worth sending to a shop that does those kind of repairs if you're phone isn't under warranty. Otherwise, being that in my case this was a for sure hardware issue, one should seriously consider barking up HTC's tree or whoever guarantees the warranty for a replacement.

Here is a link leading to the picture of the lower microphone board:

http://www.etradesupply.com/oem-htc-one-charging-port-pcb-board.html

I wonder if by chance it could have been caused by a weak connection by one of the many tiny connectors in the ribbon cable where it mates with the mainboard connector. I doubt this was the case, but being that I don't know exactly why the otherwise working microphone didn't work correctly in dial mode, and that I didn't think to test the cable theory while I had my phones apart, I may never know. (hehe, I'm not pulling my phone back apart and re-swapping mics to find out!)

Also, yes I'm back on my custom ROM, which I restored before switching mics (and still verifying that the problem still existed). All I did was power off, swap the mic board, and power back on, made a few calls to test, and was glad that everything was back to normal. I hope this post helps those of you that had / have / will have the same particular problem as I had to be better informed as to what your options are.