On both my iPhone 5 and iPad mini, noticing that when ringing up someone over FaceTime, the beeping is almost imperceptible... I remember being much more noticeable in iOS 5... And i have sound effects/ringer volume turned all the way up...
I had a similar situation. They could hear me but regardless of how loud I set the volume it faded in and out and cut off mid word etc Was extremely frustating trying to hold a conversation. I would love to find a work around for this other than use my old iPhone 4 to connect through facetime.