1) Man is that the quietest gym ever ;)
2) Your low back is remaining flat, which is the most important thing. However with your upper back / shoulders beginning to round - it's the beginning signs of you reaching your deadlift limit, with the limiting factor being the back.
To help keep the back completely extended during the lift, work on cueing yourself to stick your butt out even moreso, as you bend down to pick up the bar remember that you should be HINGING into position not just bending down to pick it up in the same fashion that your body would move to squat. As you hinge, think to yourself 'heel heavy' - sit back onto the heels. Remember also to think about arching your low back - HARD. Again, you aren't trying to hyperextend the low back, but under the stress of the loads your hamstrings and low back are in a battle to control which way your hips tilt.
If you don't already, you can start adding in either romanian deadlifts or stiff legged deadlifts with a moderate weight. You are not focusing as much on training the leg component on those lifts as much as you are focusing on keeping your full posterior chain in extension. Another supplemental lift to toss in would be low back extensions to focus on strengthening the low back for the same purposes as mentioned above (the battle of your hamstrings vs. low back).
Finally, just always remember that done correctly - it's SUPPOSED to be hard. The difficulty of the compound movement is only to your advantage.
Great progress!