Plumbing issues

I don't know anything about plumbing. I live on the third floor of a twenty-four story building. At 3am, I woke up because the toilet was making noise.

This happens sometimes if you press the handle too quickly: it'll just keep filling and filling and filling (because the flappy thing doesn't re-cover the out-hole). So the fact that it was making noise wasn't so unusual. However it was changing volume a lot, similar to what happens when the water has been turned off for a while and then turned back on again. Air in the pipes?

Anyway, I went to fix it, to stop the noise, and found that the new water coming into the toilet was brown. Eep! I went and used the other toilet (we have two) and it started filling with brown water too!

Both of them flushed just fine. They didn't clog or overflow. It's just that the water coming in was brown. As far as I could tell, the water from the tap was normal.

Throughout the day, they both got a bit clearer every time they were flushed. By afternoon, they were normal again. I called the caretaker in my building, and apparently no one else had complained about such a thing.

What could possibly cause this to happen both my toilets, and no other ones in my whole building? Should I worry about it happening again?

Thanks in advance for any advice!