HF noise is an increasing problem that plagues hams in the suburbs. Switching power supplies, solar inverters and plasma TVs are all culprits.
Here I'm plagued by occasional bad interference on 40m (but really all over HF) that I think comes from a switch mode power supply used by a neighbour. I've just built the antenna noise canceller by Terry, VK5TM and it seems to work very well.
Noise cancellers work by taking a sample of the noise, inverting the phase, matching the level with the signal and mixing them - thus cancelling the noise but leaving the signal. Here's another example where I switch it in and out:
Here's the part of the circuit that controls the phase of the noise signal that is then amplified and mixed with the main antenna signal:
I bought the board and kit of parts (AU$55) and it is a very professional package. The parts are well presented and I found none missing.
The kit went together smoothly following Terry's instructions. The only fault was mine, when powered up the relays didn't click even though the transmit LED came on - I had missed a solder joint on one of the coils.