Buzzing on AV Famicom with NESRGB mod

I've finally got round to installing an NESRGB on my Famicom AV and the picture quality appears to be fine, but I get a lot of buzzing, which I know is pretty common for Famicoms anyway, but it appears to be greater than I would usually expect.

I haven't done anything to the stock audio and haven't tried to see if using the NESRGB will fix the issue as I can't find specific instructions for using the NESRGB audio with a Famicom AV. Do I just need to connect CPU pins 1 and 2 to the NESRGB and the NESRGB to the audio out AV pin? (I assumed I would have to lift some pins or cut some traces...)