You could try using ferrites round the leads, either in the form of beads you thread the wires through or a toroide to wrap them round. Don't discard the case either as that will be part of the eventual solution.
You could try using ferrites round the leads, either in the form of beads you thread the wires through or a toroide to wrap them round. Don't discard the case either as that will be part of the eventual solution.