Boombox damage?

Hello everyone. I recently joined this community to learn more about speakers and audio. I have a big question however and if someone with speaker knowledge could answer my question it would be greatly appreciated. I recently bought an altec lansing imt810 and it is really a great boombox. Maybe not audiophile quality, but I was looking more towards volume than quality although it really does have a nice sound (at least to me) and can pump volume extremely high. I have been using it pretty often at high volumes and although I don't put bass boost on many of my songs have heavy bass. Recently while I was playing a song, a subwoofer (there are two, I don't know if it was one or both.) started playing a weird noise that definitely is not part of the song. I can not really explain it very well as I immediately turned the boombox off to prevent further damage and so did not hear what happened clearly. From what I briefly heard, I think what happened was that the subwoofer played a higher note than the original song and to just summarize it sounded very wrong. I'm not sure if this is distortion, and I would like to know if my speakers are permanently damaged or if this is just natural at high volumes. I don't think I had this problem before when I was playing the exact same song. Additional info: there are 2 horn loaded tweeters, two main drivers, and one subwoofer and the other is passive radiator. Another question I would like to know is when do you know when you are playing something too high resulting in speaker damage? I don't know anything about audio other than the basics so if anyone could answer this I would be extremely grateful. Thank you for your patience.

P.S. if this is the wrong kind of forum to ask such questions, I would like to apologize as the first forum that came up for audio was this one. If there is a better forum for my problem please link me. Thanks.

bump

thnx so much for the answer. It really helped and yes I was using it on battery power. Thnx very much!