The thing about interference pickup is that it's significance is entirely determined by the level of DSL signal you are having to deal with. Clearly very few good volts received equals potential for trouble. The thing is, the noise received further away on the line will itself be attenuated as is the signal, if it is picked up not near the house, on the other hand, noise inside the house is the absolute worst thing in the world in two respects: it itself is not attenuated, and it is being compared with the dsl signal at its weakest. I don't know how much difference a metal case might make, but sticking kit in a biscuit tin temporarily might be an interesting test, ought to ground the tin too. If it is going to make a difference anywhere it will be to me with my lovely 67 dB downstream attenuation.
@sevenlayermuddle - I wonder if there is a device that can kill the power to a socket based on smoke detection and a temperature or infra-red alarm? Having had a terrible house fire some years ago, as has a good friend of mine recently, and I have also have had a washing machine catching fire too, it's a subject dear too my heart, and it's not something you want to have in your life.