Gary RV Roamer said:
There is no inherent reason that leds themselves would generate RFI,
Actually.... There is, LED's naturally generate a very wide range of frequencies, In another time I had a friend, T.E.Hartson who along with Walt Wilson wrote an article for a magazine I happen to subscribe to. The article was a construction project, a "Gated noise source".. This is a device that spits out a very very broad spectrum electronic noise.. If you gate it (Turn it on and off at audio frequencies) and feed it to an AM radio you hear the audio (Gating) Frequency, You turn around the band, the tone does not change It never gets louder or softer.. You change bands, the tone is still there.. The unit described in the article was "FLAT' (That is the output was consistant) from around CB frequencies to MICROWAVE Ted (T stands for Ted) used it to tune up the receivers at the cable vision company he worked for, as well as his ham gear.
The noise generating device was a diode,, All diodes do this, (Generate noise) the trick is to control the diode's noise.
I built one using LEDs.. Did not work as well as Ted's but there were several compromises in my design. I will fix that one day.
Now to the original poster....
There is something called a Disc Ceramic Capicator, Radio shack sells them in the parts drawer. Pick a few in the .1 .01, .001 range, wire them in praallel and wire them across the leads on the LED, the closer to the LED's you can put 'em the better, they absorb RF enegery I'm not sure which one will do you the most good but if you should try assorted powers of 10 till you get lucky, they are low cost .