Lesson learned: if piano music suddenly starts sounding like somebody is raping the melody line with a pitchfork, check if the bass boost option on the CD player accidentally got activated.
What the hell is that option for, anyway? Unless you're listening to the ear-killing soul-destroying monstrosity some people call "music" music that's little more than noise, having just a loud bass line, I can see no reason to use the bass boost option. It completely kills any melody line the piece of music might have had.

Actually, I have a stereo that sounds like somebody is strangling a cat when the bass boost is off. On it sounds about normal.

I guess the bass boost button is so you can decide which setting sounds terrible and use the other one. Maybe the manufacturers are deaf and can't tell which is which.

'Xcuse me, some of us like our soul-killing monstrosity music. Also, even in the non-soul-killing genre, the bass line enhances music with multiple instruments + vocals.

Point - but I'm not against the bass line, I'm against boosting the bass line so much that you can't even follow the other instruments / vocals / melody. At least, that's been what the bass boost option has done to music on all the stereos and CD players I've owned (granted, not many but...) *shrug*