Distorted sound on speakers

What would be the main cause?
I've had experienced a few occasions of distorted or strained sound on my speakers. One time, it was due to loose connection on the banana connection. After the connection is secured the problem was gone.

This time, all connections are fine, but one of my speakers are producing distorted sound on certain albums, mostly on CDs. More apparent on high frequency (high female soprano), but sometimes low keys on piano. It rarely suffers problems on LPs. I switched the speaker location (left to right and right to left), but the distorted sound is always on that particular speaker.
It is not only due to high volume. Evan mid volume on certain CDs produce distorted sound. I tried all my 3 CD players, but the result is the same.

Strange thing is that it is fine on certain other CDs.

Can I safely assume that the speaker is flawed?