I have been suffering with a 'whoosing' switch mode power supply noise on the lower part of HF for the past couple of years. I traced it to a GDX intercom/door entry system's PSU, Ofcom were able to verify this recently. I notified my local Council as they're my landlord, they sent out an electrician and I gain access to the circuit board with his supervision. I fitted 3 fair-rite type 31 material ferrite clamps between the PSU and the circuit board, thus reducing the QRM by about 4 S points from an S9 to an S5. The wiring for the whole system was reradiating the QRM from about 3MHz to 13MHz. GDX is part of the Stanley group I believe. Apparently they've never came across this before and were somewhat sceptical from what the electrical inferred.