My 912 Rotax powered plane is very open to wind and engine noise. I use regular GA headsets because they are easier on my ears and are tougher than the ones I had as a "fat" ultralight. My problem is one of squelch. On the ground, at reduced power, I can use the vox setting on my intercom with no problem. At takeoff or cruise power, I have to switch over to PTT. It is very inconvenient especially for the passengers. I do have an intercom built for open aircraft; but, I think the frequency of my engine might be causing the problem. It is a much higher pitch than a GA engine. I have tried Mic Muffs; but the squelch stays maxed out. I thought about making my own mic muffs with a very reduced set of holes; but, I haven't done it yet. My radios actually sound pretty clear when I broadcast; but, of course, they are on a different PTT. Any help or thoughts would be appreciated.