I am in the same boat. Issues started 4 days ago. My glass isn't broken only the internal speaker (ear speaker). I am in the process of finding a screw driver to open things up.
Ok - I believe I have sorted the issue. I used the tear down guide on the iFixit site (Motorola Atrix 4G Teardown) and the video on YouTube (http://www.youtube.com/watch?v=TbR56jSpl...) to open up the phone. I only had to take it to the point where you see the ribbons attach to the motherboard.
The ribbon cable that connected to the bottom end of the mother board was unattached. I tried twice to just reattached and reconnect things but found that it required a little black electical tape to hold it in place.
It is still early but the repair seems to be worked. The loose connection would make sense since the problem would come and go.
Big thanks to iFixIt for the tear down!