Recently I noticed one source of radio interference on 40 meter was the
lighting in our bathroom. There are two sets of lights in the bathroom,
one with a switch which causes heavy interference and one with a dimmer.
The lights in the bathroom are all 12volt based and the transformers are
in a weird corner above the bathroom, but accessible for me. So I found out
the "osram halotronic htm 70" electronic transformers (the specs read
like switching power supplies) are quite audible on the 40 meter band. The
other two a lot less than the switched one.
Time to complain to Osram and/or replace them.
The Osram Halotronic HTM 70 specifications
at Osram say the maximum length of the wire after the
transformer is 2 meters to keep RF interference below acceptible levels,
I am not completely sure the complete wires until the lamps are shorter
than that, so it may also be an installation fault.
Searching for "osram halotronic htm 70 interference" finds this interesting
Installation LED Leuchten in Spanndecke
Aber auch wenn "nur" der Meßwagen der Bundesnetzagentur vorbeikommt und Deine Konstruktion kostenpflichtig stillegt, kommt wenig Freude auf.
The German Bundesnetzagentur is a lot stricter in finding and stopping
interference to amateur bands.