I had an interference issue on 118.300MHz. Scanner and Icom Aviation Transciever could not be "squelched up" as they were picking up strange noise on that channel.
Tracked it down to the Carrier gas furnace of all things, and it was being radiated via the thermostat wiring! Coming from the furnace processor/controller board.
The fix was something Motorola, Inc. recommends: ferrite beads, the clamp-on type. 3 beads wiped out the interference, so I put 4 on.
If you search the internet, be aware there is a lot of bad info about these things. Put them as close to the source of the interference as possible, power wiring, cables, wherever it comes from (just start turning things off one at a time until the problem dissapears, then you've got it).
New info: Learned from a professional electrical engineer that, if it is possible, put 2 or more turns of the offending cable through the bead as the attenuation of the radiated interference gets better as the SQUARE of the number of turns put through the ferrite core. The SQUARE of the number of turns! ghods, this is some really good stuff! Depends if you have some slack or can disconnect the cable - I could not.
Photos of my fix attached.