Help! Radio interference when using phone charger

[Mazda6JW]

Hope someone can help - my standard radio works fine, but if I plug my phone charger into the 12v socket next to the ash tray or the one in the centre storage container under the armrest, it crackles and gets interference - it also does it when the rear window wiper is moving - has anyone experienced this and found a way to stop it happening?

Mazda6 Mk2 2008 GH 2.0 Diesel Sport