I hate it when people are looking for something for you and keep you on speakerphone rather than hold. I don't want to hear papers shuffling.
or you hear them breathing while the phone is still up to their mouths and they want you to hold on while they look for what they need. i hate that.
... or if they're eating something that sounds like cereal and you can hear the mushing and sloshing... that's nasty.
OMG YES!!!! or their chewing gum...OMG