The tweeter on my speaker has a crater...Help

Sorry for the long post, but I hope somebody can help:
I noticed today when I took the grills off from my Monitor Audio Silver 6 speakers, that the tweeter on the one on the right has a large crater, as if it's been pushed in by someone. Now I can't tell if my kids could have banged against it by accident. They are young but very mindful of my audio equipment.
So could it be something else that could have caused the tweeter to distort out of shape? I remember one thing probably about 6 weeks or so ago, listening to a Miles album, that it sounded quite horrible and the trumpet was screeching in my ears. After a few minutes I couldn't pretend to be enjoying myself and had to turn it off. I got busy and didn't think about it any more about it at that time. But today after I found out the problem, just out of curiosity I listend to a Dave Brubeck SACD, and I couldn't tell if anything was wrong (but then I am not very experienced on the listening side of things).

So anyone have any ideas what could cause something like that to happen? And what kind of problems warranty will cover? Money is pretty tight right now so this is very disappointing if warranty does not cover it. I listen at moderate levels, nothing very loud at all. I have the Rotel 1060 amp and the RCD-961 CD player and the Phillips 963SA dvd/sacd player.

Thanks for any help.