[PaulR]

I greatly improved modulation hum from power supplies around the neighbourhood by putting a 0.1uf class x capacitor across mains live and neutral inside a couple of plug tops. It didn't stop it all but it greatly helped. You can move the plugs to different sockets around the house to get the best effect. The hum was the worst when receiving MW from my pantry transmitter.

Oddly it seems to work better than putting the cap inside the radio itself.

It may not help but the cost of trying isn't great. Just be aware that if you touch the pins of the plug soon after unplugging it the charge on the capacitor will give you a little nip. You could add a resistor to discharge it but there isn't a lot of room.