Here's one to add to the RFI noise list as well:
Recently I had a "SCHEETZ-SCHEETZ-ZZZTTT" 40 over 9 type of periodic noise suddenly appear around 3885. Turns out it was simply strongest there but also had some RFI on 7.150 as well but down about 3dB there.
I turned off all circuit breakers one at a time for a minute each, no luck.
I took my G3 recever outside and around the house to the power transformer box, nothing. The farther away from the house, the lower the noise.
I came back into the house and the noise was stronger. Okay, extend the antenna and put the receiver near the smoke detectors. Nothing. Placed it near the Modem and cable coaxes, not much there. I placed the receiver near the LED light bulbs and the CFL's around the house and - notta.
I happened to turn around in the family room and the noise increases as I go toward the grandkids portable DVD player which was charging on the stair well. Bingo!
I unplugged the wallwart and the noise started to reduce in intensity. Apparently, even after unplugging, this critter was still creating noise. After about 7 minutes, the noise at the DVD walwart finally died out. To top it off, the DVD charger has a ferrite slug on it just before it enters the back of the DVD, but injects RFI through the 120V plug.
I suspect the charger has a capacitor that powers a "keep-alive" circuit going for a few minutes until complete discharge.
Phil - Ac0OB