What am I hearing???

Good explanation Stehno.

One reason for time smearing in cables (or any device passing an electrical signal) is the dielectric effect of the insulation layer. Since no insulation except a vacuum is perfect, some of the signal will travel through the insulation instead of through the wire itself. The propagation speed of the signal through different materials is different, so by the time it gets to the other end of the cable the effects can be audible. It is easily audible if you compare, for example, zip cord to a decent speaker cable.

Mechanical time smearing often occurs in LP playback. TT designers go to great lengths (or should do anyway) to make sure their decks run at perfectly stable speed. Any deviation is audible in instrumental timbres long before it gets to the point of pitch-wavering.

Fbi - you say this problem is only on SOME CD's. Any chance you're hearing tape stretch or tape deck motor irregularities from original analog recordings of less than stellar quality? Try the suspect CD's on another player before assuming there's something wrong with yours.

Calanctus,
I'm one of those who offered an explanation of dielectric effect in cables causing time smearing, but I was only responding to Stehno's mention of that effect. I did not mean to imply this could cause piano note warbling. Sorry if I was unclear about that.

I quite agree with Bomarc that cable time smearing, while often audible, could never cause note warbling. The usual audible effects of time smearing in cables are harshness, haziness and the smearing of multiple voices into a homogenous mass of sound. Pitch change is never a result IME.

I also agree with Bomarc that laser problems, transport speed irregularities and non-concentric CD's are not to blame. Neither is jitter. A CD player is not a turntable, digital is not analog. I've already suggested tape stretch or speed irregularities in the original (analog) recording and mastering equipment, as well as a way to test that hypothesis.