Ok here's what I have. I have an older Autocom AVM system, just music and aux inputs no intercom. I have a Zumo 660 running into it and a Valentine 1. I'm using in ear monitors, made a custom adaptor for the 3.5 mini jack. It all works great, no noise ( have both V1 and Zumo on Autocom isolated leads) I've got plenty of volume, all is fine..Until I hit the Horn... BRRZZZT.. nasty noise. It doesn't do it with the Autocom headset, only with the in-ears monitors. I have replaced the stock horn with dual Fiamms wired up with Eastern Beaver relay. I'm thinking that an in line 12 volt noise filter or ground isolator for the Autocom should do the trick. Anyone care to offer their opinions, all are appreciated, thanks.