About two summers ago, they replaced the carpet in the hallways outside my apartment. They started promptly at 7am every single day. I'm not sure exactly how they did it or what kind of machines they used for it, but it was LOUD and it woke me up every time. My bed is situated against a wall the faces one of these hallways, so at times that wall was the only seperation between me and the machine, and the wall is not very sound proof. In fact, it's useless for burying sound. It was like having a machine running right next to my face while I tried to sleep. This went on for about 2 months straight, even on the weekends occasionally.
Aside from that, there's a maintenance office across the hall from my apartment, so the staff is frequently entering and exiting and all the doors they go through are not quiet. They also bicker with each other constantly and I can hear that, too. It seems like that little foyer spot right on the other side of my bedroom wall is where they gather to bullshit about their personal lives at 8am. It doesn't keep me from sleeping anymore, but if they're loud enough I will wake up briefly and then fall back to sleep.
I don't wake up for work until 10am, so on the worst days I'd deal with constant noise for 3 hours of my sleep.
I would actually prefer living in one of my old places near a train station where they put all the trains cars together before they leave on their routes. If you've never seen or heard the process of train car being attached to each other, it's loud like an explosion. This place was maybe 2 blocks from where I slept and when they put the cars together it would make an ultra loud "BANG!" and you could hear all the cars rattle. The first time I heard it, it instantly woke me from a dead sleep. I was positive I'd never be able to live there long because of that noise, but within two weeks I didn't even notice it anymore. They put these trains together 24 hours a day.
The coolest thing though was when they'd attach train cars like a half mile down the track, so you'd hear the big bang rather faintly, but then you could hear the rattle of the cars getting closer and then pass by as it made it's way through the entire train. That always tripped me out.
In short, fuck loud noises while sleeping.