Grado Sonata pops out of grooves during crescendos

You said you've set VTF to .1g over the level recommended by VPI. That doesn't make sense to me. VTF ranges are specified by the cartridge maker for each particular cartridge, not by the TT or arm maker. They have no idea what cartridge you might use.

Check Grado's VTF spec for the Sonata and try something near or at the top of the range. It wouldn't hurt to double check all your setup parameters, but that's where I'd start.

It's conceiveable you have a resonance problem that's only excited by certain passages on a few records. The best way to check that is with the resonance tests on the HFNRR test record. If your resonances are higher than 15Hz or so then you might (rarely) experience the problem you describe. If that's the case you'll need to add some weight to the headshell to bring resonace freq's to < 15Hz.

In any case, I wouldn't play any records until I solved the problem. Even if the cartridge is staying in the groove there's a good chance that it's mistracking enough to damage your vinyl.

Doug, the reason VPI suggests that owners add an additional .1 gram to the cartridge manufacturers specified tracking force is because VPI arms do not incorporate any anti-skating mechanism. If I understand their design philosophy, they feel that less harm is done by this slight increase than would be done by the forces applied in an anti-skating scheme. The Grado Sonata is one of two cartridges that VPI sells and sets up for owners at the factory, so they are very familiar with this one. Thanks for the suggestion regarding a possible resonance problem. I just found it very peculiar that this problem occurs only on one out of hundreds of lps. I'll double check tracking force again.

Photon,
Thanks for the explanation, understood. Of course that just makes the problem more mysterious. :-( Do you ever see the infamous "Grado wobble"? That might be related to the resonance idea.

Yup, I definitely have had intimate familiarity with the "wobble." Several lps with slight warps on the perimeter excite the cartridge suspension and the wobble dance starts. I'll look closely while playing the suspect record & see if there's a connection. Will.