Hi Kitz,
Many thanks for your thoughts.
I do occasionally cluck on about dI/dt but it leaves many people cold.
I have no absolute proof yet, but a very strong suspicion, as the cross talk was often worse in the very early morning in an area otherwise all asleep at that time.
The proof we have is that by shortening the next door's twin BT overhead line, which had been brought down by building operations and was left in a heap on the ground, the noise spikes decreased dramatically.
Within a few weeks new lines are to be installed in the adjacent house and I will do my utmost to get BT to re-route the dropwire away from the noise source cables.
If that fails perhaps we'll have to do as you say but only as a last resort. The user is an avid downloader and the difference between a bRAS of 500 and 750 is of great importance for him.
Kind regards,
Walter