[Porboynz]

I must have been just plain lucky, I ran a stock CDI with standard plug leads and a Kenwood head unit. No special filters, but the CDI is earthed as is the fuse/relay panel and no noise on the radio or cassette. (Well, there is/was plenty of noise, but that was the RS style muffler, thats a good noise, right?) Maybe your head unit is a little susceptible to RF noise? The CDI box should not radiate noise but those plug wires might. Of course that does not explain why the Permatune is silent.