I hear nothing in my sleep. Dad could be right out my window mowing the lawn at 6:00 am on a Saturday morning and I would not hear it. However I do hear my alarm go off everymorning, I have it on LOUD as well as making my cellphone light come on. More times than not, it is the light from my cell phone that wakes me up rather than the alarm. Mom says she can hear my alarm go off all the way downstairs from my bedroom, and the bedroom door is closed, so I must have a really loud alarm. Oddly though, my DD is so used to it going off that anymore she'll stir when it goes off, but as soon as I shut it off, she just blinks then goes right back to sleep. She is a very deep sleeper, sometimes it takes a lot to wake her up. Occassionally though she'll wake up and not be able to go back to sleep, so I take her downstairs to let her sleep with my mom while I head off to work.
Another thing is, my mom has a backup alarm in her room so that if I should not hear my alarm and not wake up, her's is set to go off 15 minutes after mine does and if I'm not up and around by the time her alarm goes off, she usually comes and wakes me up to make sure I get up and get to work on time. 90% of the time though I do get up with my alarm but there's been 2 or 3 times that mom has had to come wake me up.
As far as hearing in my dreams, it is about the same as what I hear during the day. The speech I hear is mostly garbled by sound alone, so I have to speech read, in my dreams it is the same way although in my dreams I tend not fuss about what was said as its usually irrelevant to my day-to-day living.