We have used Sena 20s for our helmet to helmet intercom and get clear conversations all the time. However, listening to anything coming from the SM10 to our helmets does have static - not so bad that you cannot listen to the music, but certainly annoying to the point we just prefer not to use it anymore.
We have since switched just this season to the new Sena SRL comm system built into the Shoei modular helmets and they have the same issue with the SM10.
I suspected it had something to do with the source into the SM10 coming from the spyder but did not have a separate MP3 player to try that - its encouraging that that seems to clear it up for you.

We may look into going that route, not sure because we have done so many miles and mult-day trips without music now we kind'o don't really miss it.


On another note, we love our new Shoei modular helmets with the built-in Sena SRL. Worth checking out if you are ever in the market for that type of helmet.