faint precession of sound on vinyl

Actually, you are totally right. I checked out and I heard it on an older recording of a Bach cantata on CD. It is not a vinyl thing after all. I guess much of the time they eliminate it from the master tape when they make a digital transfer, thus it is less frequent on CD.

I can pull out a dozen CDs that have pre-echo. It's the master tape, not the format.

It is almost always groove-to-groove interference. This is easily verified by timing the amount of pre-echo. If it's 1.8 seconds it is a LP problem. Mag tape print-through is also real, but usually requires storage of the tape for years without rewind, and the timing will vary with tape speed and how much tape remains on the reel.

Pre-echo can be eliminated by wide groove spacing, but that drasticly reduces playing time. So groove spacing is dynamically varied as the record is cut according to the music signal amplitude. As always there is a compromise, and the grooves are kept as close together as possible, accepting a small amount of pre-echo that only audiophiles will complain about.

The first Led Zep album on LP has quite a bit of this prior to each song. Never heard the CD. I once read that it was because the singer was in one room and the mic was in another for echo purposes, and the mic was picking up the original vocal in real time before it registered on the tape from the speakers. Always thought that sounded funny but who knows?

I used to think this was a problem with my cartridge alignment or tracking error of some sort. It seemed like when I switched to the 10.5i arm from the 9 sig it decreased. Maybe it only seemed that way. Thanks for the explanations on something I've always wondered about.