Hi Brett.. on all the CDI's I run here, the oscillations are either at such a high frequency that you can't hear it or it's the fact that it is a happy circuit without audible hum or noise. In other words it is efficiently using the current. If you have an actual noise coming from it, there may be excess current draw. I use only CDI style coils. I tried a home made coil but couldn't get it to keep working because of the high voltages (15-20,000 volts). I wasn't interested in making excessive voltages because of using them for Radio Control planes..it causes alot of unwanted RF energy (noise to the radio control reciever). I never run shielded wiring either.. nothing on the sparkplug wire..just a normal seperation between the systems of 6 inches. That seemed to work for the purposes here. Charlie can tell you first hand about RF signals and radio recievers..
If you need that high of a voltage, add more turns to the toroid secondary..I think you are looking for the voltage to gain reliability at higher rpm's than we need with our planes..
Hope this info helps..all things considered, you have an exceptional system with higher voltage requirements. All I can say is experiment with the windings..

John