Advice on mistracking or some problem

Well, at least you know it is not the cartridge. You're right, if the distortion remained on the same channel even after changing L/R, then it is post table.

Distortion stayed on same channel-wise despite switching input into receiver, as suggested by Headsnappin. I guess this suggests something post-turntable. Hmmmmm.

How often do you clean your stylus? Do a discussion forum search for Mr. Clean Magic Eraser. Magic Eraser can be purchased in the cleaning products dept of a grocery store. They are white, ultrafine textured scouring sponges. A small piece can be cut out with a razor blade or exacto knife and glued to the end of a popsicle stick. It is placed flat and the stylus is raised and lowered several times into the magic eraser, which scours off deposits. Sometimes I get a similar sounding noise, but after taking a couple of minutes to clean the stylus it solves the problem. I usually clean the stylus about every 5 LP sides or so. Take some care so the stylus does not get caught in the sponge (hold the sponge still while raising/lowering the stylus), and perform the task so that any debris/sponge residue does not end up on the platter. I also use a stylus brush to remove any potential sponge debris from the stylus afterwards. The sponges are an almost microscopic honeycomb-like texture, and though I have never seen residue come off the sponge, I suppose it could happen.

Did you recently change cartridges?

This is on all lps, not just old ones. It is not always just at the beginning of the lp, but usually is. Good idea on switching the inputs, I will try that. Possible this is the receiver, I suppose, since it seems to happen more often at the beginning of a listening session and less after things have "warmed up". Last night though it was just terrible, happened often and and all points on a record. Did not lessen with warm up. It never happens, however, using a cd player with the aux input. Could it be a receiver problem limited to phono inputs? Receiver is a solid state Pioneer SX-828 from 1973, no tubes. Thanks everyone for the ideas.

Does it happen on all your LPs? Just new pressings or older pressings too?

Have you tried switching the left and right inputs and, if so, does it switch? If not, it is something down stream of the turntable.

I would have to agree with you that the setup is probably good. where it not, the problem would persist throughout the playing and would be continuous. If I am reading you correctly, the problem appears in the beginning, goes on for a bit(20-60 sec.) and then is gone and everything is fine. That argues against setup errors. My guess is that the signal is hitting something, perhaps in the receiver, that takes a bit for it to get into adjustment. Are there tubes in your receiver?
If so, one may be going out in the phono section, or may need to be cleaned. Does it happen for each record, no matter how many you play? Or is it just for the first few, say for the first half hour or so of playing, enough time for the receiver to warm up?
Have you checked the clips on the cartridge? One could be partially loose and at the furthest out point may be more stressed. Same could apply to the phono cable.
Hope this helps for ideas.
Michael

I have tried VTF between 1.6 and 2.2. VTA is maybe slightly lower on pivot end. I'll be getting another cartridge to test with soon. Anti-skate doesn't seem to make any difference.

Strange that this happens at the beginning of an LP. If it really is skating, then it would more likely happen in the inner grooves and louder passages.

What VTF are you using? How is the VTA? And do you have another cartridge to test with?

Did you play with anti-skate?