HNG64 video interference

I am seeing noise on the video output of my Rev1 HNG64, and the source is very obviously the audio. The noise matches up with the beat of the audio, and adjusting the volume pot increases and decreases the noise as one might expect. Setting the pot very low minimizes the issue, and unplugging the audio obviously eliminates it entirely. Other than that, the board works perfectly.

I am not 100% sure the speaker harness is wired correctly, since the manual contradicts itself, but the audio seems to work ok. So I don't know. Has anyone run into this before?

So I messed around with this some on my US board.

The very poorly scanned manual schematics show this wiring:
1 R+
2 L+
3 R-
4 L-

This is also the wiring shown on a sticker that seems to have been included on Japanese Rev1 boards. I have an audio harness wired this way, and I get significant noise on the video, likely due to a ground issue. Audio seems to work, and I seem to get some stereo separation in the sound test. But not much.

The same manual also includes this completely different wiring diagram in the connector table:
1 R-
2 R+
3 L-
4 L+

I wired a second harness this way and I don't get any video noise. Which is great, but I don't seem to have much (if any) stereo separation at all in the sound test. Which is weird.

Bottom line, I don't know how this should be wired. I honestly wouldn't put it past SNK to have wired the Japanese and US boards differently, but at this point, I am probably going to need to dismantle the unit and start tracing signals on the PCB with a meter.

If anyone is curious, I also measured the current draw (using a FFWA cart), and at least on my unit with this game, it divides the 5V current fairly evenly between the JAMMA connector and the JST connector. I measure about 0.9A on each of the four 5V wires during attract mode. I am sure the JAMMA connector can handle 2A on each 5V input, but adding some extra power lines certainly can't hurt.