I have a call quality issue. My voice sounds terrible to the person I'm talking to. I've left myself voicemails to confirm.
This isn't necessarily a problem with the phone. I think most noise cancelling systems are confused by the specific tone of my voice, and end up trying to cancel pieces of it.
I had the same issue on the Galaxy S3. The S3 had a setting in the dialer app to disable noise reduction and that fixed my issue. I have not found a setting like that on the N5.
As a test, I put my finger over the noise cancelling microphone and left myself a voicemail and I think it sounded better. But that was only 1 test, so I'm not certain about that yet.