The digital sources in the system that has the turntable, my basement system, do not show this problem. I believe that narrows the issue down to the turntable, arm, cartridge/stylus, phono pre amp, or perhaps the LPs.
I have hardly listened to the analog system for the last 2 months, primarily because we were out of town caring for my mother in law who was in hospice at home. I don’t recall noticing the problem previously.
Regarding the cartridge alignment, why would that only cause an issue during the loudest passages? I had purchased the table from Music Direct in Chicago and had them mount the cartridge. I don’t have the tools to do an alignment and it’s been half a century since I’ve done this, and frankly I don’t trust my eyesight to much at this point to detect a minor misalignment. I have another dealer 20 miles away who will check it if I bring it in, and I might do that, but as a last resort.
The record that really made me notice this (Jascha Horenstein/London Symphony Orchestra in Mahler Third Symphony) hasn’t gotten the deluxe cleaning treatment. I have my LPs cleaned by a local guy with an Ultrasound machine who gives a bulk discount. I am waiting to take possession of some LPs that my in laws possessed and have him do the lot so that might take several weeks. I’ll spin some other cleaner LPs in the interim