In reply to a post by gomezz:

Interestingly the three sources of inteference I have had to deal with in my house were my old laptop mains lead, the power supply for my christmas lights and having a phone plugged into the bedroom exgtension (now use a cordless). On top of that I cannot have my DAB radio plugged into the same extension lead as my hi-fi amp without getting earth loop hum through the speakers.

reply to old post but... Problem with extension may be it is wired from junction box before the master. If so, disconnect it. It will be terrible with a phone plugged in, but also quite bad even without. You may get quite a bit of extra speed.