Thank you all for the friendly and helpful comments!!! It looks like I've joined a very positive community.
As I've said, this is definitely a two sided coin. On the one hand, when you knowingly move into a place where you share walls, a floor, and a ceiling with other people, "noise" is just a part of life. There are some folks out their who are completely inconsiderate and will crank up the music and stomp around to their heart's content. Others, like myself, do their best to keep the noise at a minimum, but unfortunately, even despite my best efforts, it's not always fully in my control.
Health-wise, I'm in no condition to move. Financially, it would be very difficult to pay a company to move for me. Not to mention the stress on the cats, bill transfers, and so on. In short, it really isn't an option.
The floors are carpeted, though they don't seem to provide much resistance to the sound. And they do have cat trees, but that's part of the problem. It's not just the running around. It's jumping off the highest platforms in the house and hitting the floor with a THUD.
I don't have cable, but I'll see if I can find a way to loop a movie in the background to see if the human sounds help. I think the biggest thing is that they just get bored when I'm gone and very excited when I get home. Like I said, though, they're just being kittens and I want them to do as they please and be happy. If it weren't for the neighbors beneath me, I'd let them run around as much as they wanted