I pulled down the 40m loop entirely to inspect it after sweeping SWR and finding nothing there. Found nothing physically wrong, really. I added some electrical tape where water was getting into the PL259 threads at the balun, and soldered a connection that was just crimped. Checked the 80 feet of coax with a NanoVNA, and got 1.95 db of loss at 50 mhz, and about 1db at 15 mhz. Normal for RG-8X with a GDT in it.
I found a couple issues in the shack: A PL259 jumper cable had a loose ground connection to the shield, and a right angle BNC to PL259 jumper was shorting out or something depending on position. I could turn the interference/noise on and off by moving the cables around. Hard to say if it was one or both, as they both plugged into an MFJ SDR switch, and thus moving one kinda moved the other. I replaced both cables, and signals were back to as they used to be. 10m WSPR SNRs improved by 25+ db, back to where they were before 10/13.
I've vowed to use more flexible (smaller cable) jumpers where I can in the future, as the thicker ones are wrenching around light things they're attached to. So more 6-12" RG-174 jumpers instead of RG-58 or RG8-X.
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