PAL SNES buzzing with SCART RGB cable, a bit out of ideas

[ASDR]

I'd need some advice on how to fix my el cheapo cable. I have a PAL 2-Chip SNES. I got a crappy China SCART RGB cable for it:



Cable was wired exactly like this:



I verified all connections and resistors. Looks good.

Now, I got the predictable results with this cable. Pretty bad checkerboarding / diagonal lines and audio buzz.

I opened up the console side connector and changed the sync line from composite video to luma. That fixed the checkerboarding. Video looks pretty clean now.

Unfortunately, it still had the audio buzz. If I use the original Nintendo composite video cable, audio is fine.

I figured even with composite gone there's still interference going into the audio lines somehow. I disconnected the Audio LR wires in the cable and routed a pair of conductors externally for the audio:



Did absolutely nothing, there's still a very loud buzzing and other interference.

I guess I can't really do more for the audio lines than running them outside the main cable, the only thing still in the cable is the shared ground. All ground pins seem to be hooked up, all connected to one ground on the console side, like in the wiring diagram. I noticed the shield of the SCART connector isn't connected.

What do I need to do to this cable to get clean audio?

Thanks!

[ASDR]

I thought I'd try also isolating the ground wire. So I just took a single conductor and replaced the ground wire from the cable with it. Now the audio buzz is much reduced, but the RGB picture looks real bad. Blurry, horizontally. Not just the normal 2-CHIP blur, but way worse than before. Sigh.

Any suggestions?