Have you earthed the metal faceplate to it's earth terminal?
This is important.
Two ways of doing it;
1) Best way - fit an earth wire between earth terminal on back box and earth terminal on faceplate. This ensures both the box and faceplate are earthed, even if the faceplate is loosened off the wall.
2) Easy way - remove all the earth wires from the back box, and place all of them in the earth terminal of the metal faceplate. The faceplate will be earthed at all times, the box only earthed when faceplate is screwed to the wall, as it it would usually be.
Either way acceptable, first way best if you can find a piece of suitable wire.
This is important.
Two ways of doing it;
1) Best way - fit an earth wire between earth terminal on back box and earth terminal on faceplate. This ensures both the box and faceplate are earthed, even if the faceplate is loosened off the wall.
2) Easy way - remove all the earth wires from the back box, and place all of them in the earth terminal of the metal faceplate. The faceplate will be earthed at all times, the box only earthed when faceplate is screwed to the wall, as it it would usually be.
Either way acceptable, first way best if you can find a piece of suitable wire.