RT 16 distortion in mid

CTDiesel

I have a set of RT16's that I got from my friends a few years ago. They bought them brand new back in the mid 90's. Just today I was listening to some music and not too many songs into it I detected an odd sound that I thought was something other than the speaker, but upon closer inspection I discovered it to be one of the mids. It's distorting, and I don't really know exactly how to describe it though. I used these quite a bit the first several months that I had them, but never played them really loud....certainly not more than they could handle. The previous owners never abused them either. I'm wondering what it might be and if there is a way to repair whatever could be going wrong? These are fantastic speakers and I most certainly do no want to and really cannot afford to replace one/them. Do I need to remove the mid for inspection?