Auto trans stumper

OK, an update on this.

Last time, I got underneath and was having the wife shift it while I listened/felt for the source...and the source stopped.

Until yesterday.

Yesterday, while towing, it had a phase of doing this 15-16 times and since I backing with trailer, it did it (lightly) every time from D to R and back. But, this was at night, and I noticed something; when it happens, the headlights dim briefly.

Manually operating the starter while in neutral matches the sound an light effects perfectly.

I'm 99.9% convinced it is the starter...so why? Last time I pulled the column apart and found no chafed wires and all I can think is the shift linkage chafing a wire, unless maybe the issue is in the neutral safety switch or solenoid/relay circuit somewhere?