It was a perception once (and in some cases still is) that 2.4 will prevent RF interference. Not so. Maybe your interference was always there but "masked" by PCM. i guess you are best off again starting with the basics. Check the plug cap is tight, R type plug, no metal to metal contacts, place Rx as far from the CDI as possible etc etc.
Good luck with it all, I know its VERY fustrating, I went through it some time back. Let us know what you come up with.