Some interconnect cables come with ferrites already installed. I have seen a number of them from various manufacturers.
I recently bought an OPPO BDP-95 Blu-Ray player, and the HDMI cable supplied with it had ferrites built in. These will be seen as large cylindrical bulges around the cable near either end (about 1 inch in diameter).
As the gentleman said, you can buy these at Radio Shack and clamp them around the Interconnects at either end. These should be quite effective at reducing RFI. Ferrites come in several types with different permeabilities which make them most effective in certain frequency ranges. The #43 ferrite material works best from 30 to 500 Mhz, and the #77 material is best for 3 to 30 Mhz.
Unfortunately, these are not always identified that way, but the most common is #43 and it will probably be what Radio Shack sells (#273-067).
You can buy these much cheaper at Mouser Electronics; they sell essentially the exact same item as above for 61 cents each, or 10 for $4.70 (part #28A2005-OA2). (this one is for cables up to 0.14 inches diameter; for cables up to 0.26 inches diameter use part # 26A2913-OA2; other sizes are also available).
Another thing that sometimes works is to buy a replacement AC plug from the hardware store and attach a .01 microfarad 400 volt non-polarized capacitor to it, connecting the capacitor leads to the two power connections. Plug this into an AC outlet on the same circuit as the equipment, and it will eliminate RFI on that AC circuit.
Speaker cables are almost never involved in this type of problem, because any RFI they pick up is at too low a level and too high a frequency to be an issue. It needs to be picked up at a point in the amplifier circuit where it gets amplified to a great degree and rectified into an audio frequency, thus becoming audible.
I have been a ham radio operator for 50 years and have had to deal with dozens of cases where people needed relief from RFI produced by a neighbor's transmitter, so my experience at solving these problems successfully is extensive. There are several specific techniques that are used successfully, depending on the specifics of the case. I hold an FCC commercial license and taught communications electronics for 30 years. I currently am a commercial communications consultant to several major system operators for RFI and intermodulation issues at cell sites and in other communications systems.
Putting ferrites at both ends of all of your interconnects is the first step I would recommend (about 6 inches from each end).
Originally Posted by kenglish
If you are picking up an FM station, it's going to be somewhere in the 88-108 MHz range, which is within the band (about 25-250) that common ferrite cores operate. Try a couple of them on the power cord, close to the amplifier, with only the speakers connected (and power, of course). That will tell you if it's coming in via the AC power.
If that doesn't cure it, try one or two on each (at the same time) of the cables...speaker (L), speaker (R), and the power cord.
You can buy them at Radio Shack:http://www.radioshack.com/product/in...ductId=2103222http://www.radioshack.com/product/in...ductId=2996360
(Two different sized holes for the cables)
There are different "mixes" of ferrites for other frequencies, such as AM and HF radio (below 30 MHz), and UHF/microwave (above 200 MHz), which have to be ordered through a major electronic parts supplier....not usually Radio Shack, etc.
What station is it? You could be close to a low-power station, and not even know it.