Hi Lafountain
I had a nightmare trying to sort out my Galaxy S3 with its Mic Problem.  When I spoke on the phone people could not hear me clearly.  I tried everything
on all the forums to resolve my problem but in vain, After much thinking I went about systematically excluding possibilities of things that may interfere, until
I FINALLY got it Solved.  Now I do realise that different solutions helped different people, I trust my experience will help others.
What I tried which did not help me : 
1. Reset the phone
2. Cleaned the hole at the bottom of the phone
3. Disabled the Secondary Mic ( At top of phone ) which plays a role in clearing background noise
What Helped and I will explain my Logic.
I went into the Settings > Motion > 
Made sure everything that i felt was linked to the PROXIMITY SENSOR was disabled, as my thinking was the
muffled or muted sound of the Mic may be associated with a glitch that kicked in when the phone Proximity detected 
something close ( my face when talking) 
Switched off 
> Turn Over to Mute
> Palm Touch to mute
And That was it , Mic Mic was restored to full function
Hope this helps.