When people mutter. DH does it constantly and it drives me absolutely round the bend. I have to make him repeat everything 3 times. And I only hear him when he shouts. So I ask him kindly not to shout as it alarms DS and he goes back to mumbling under his breath again. 
I hear you. It's gotten to the point where I'm starting to wonder if I'm the one with a hearing problem or if it could be that ALL of my family members mutter. Sometimes when I'm really exasperated I pull a Willy Wonka (Johnny Depp version) and say "Mumbler" when they mutter.
It's really annoying when I ask my eldest to repeat himself and he only repeats part of his sentence.
"muttermuttermutter oatmeal cookies?"
"You muttered, what did you say?"
"Oatmeal cookies."
"What about them?"
"You know, the ones in the kitchen?"
"And what about them?"
"The oatmeal cookies!!" Gaaaaah!!!!
I've started telling them that if they don't make themselves heard, they're not getting what they ask for.