Mega Drive 1 picks up FM radio, when using the headphone out.

Just finished stereo modding my Mega Drive 1, which turned out great. As I was testing stuff I wanted to compare the noise you can hear that's relative to the graphics on the screen (as far as I know there's no way to completely get rid of this), to the original headphone out.

So I plugged in my headphones, had the MCD1 running with the BIOS menu (no sound), headphone volume turned all the way down, and I could hear some very faint music, with lyrics! I kept listening, and realised that this was the local radio station being picked up by the Mega Drive for some reason.

I've tried isolating the console from the rest of my setup, but this "problem" persists. Adjusting the volume slider does not increase the volume of the radio signal, it only makes the noise from the console much higher.

The volume from the radio station seems to vary, it's much lower now than when I originally noticed it about half an hour ago.

What could be causing this? The audio is perfectly fine when not using the headphone out, so it's no problem really, just curious as I found this quite funny

 

Does it still do it if you remove the MegaCD? Are you using the RF video output? Did you remove any shielding?

 

It happens without the MCD attached too. The RF module has been removed in favor of ArcadeTV's RGB bypass mod.

The bottom RF shield is not installed at the moment (need to make cuts for wires), the top one is.
I wonder if this will make a huge difference as the metal plate that's needed to attach the MCD is grounded too and roughly in the same position.

 

You should look at fixing the issue with only the MD first, then check for problems with the MCD shielding later.
So something in your setup picks up FM radio signals that make it into the audio amplifier of the MD.
It could be your cables, old capacitors in the MD or any other thing. Try a different power adapter!

 

Okay if old capacitors could cause this, this may be the issue as I have yet to replace those

The signal could still be heard without the RGB cable plugged in.