Super Famicom loud hum

I have a Super Famicom with a loud humming sound through the speakers on my TV. I am using a screened RGB scart cable that works perfectly (no noise) with other SFC and NTSC SNES consoles. I have experienced the common buzzing sound from unscreened cables before and this humming sound is a lot deeper.
Could it be an issue with the S-SMP?
There is also a small graphical glitch towards the bottom centre of the image. Is this related or likely a separate issue with the RAM chips or encoder?

 

I tried swapping the encoder for one from an otherwise broken console, this resulted in audio disappearing but the glitches remain. I removed this encoder and checked that all the pads and traces were still intact and reinstalled the original encoder, and the audio is still absent.
I replaced the vram chips (one at a time) and the glitches are exactly the same as before. I will try the sram next and then the s smp, or maybe just give up.

 

Have you checked the capacitors?

 

I replaced all the caps apart from the 2 33uF as I don't have any atm. I have now replaced the wram and the problem persists.
If it is something on the underside then I am lost, all that lacquer doesn't help when looking for potential problems.