Thanks Abid - I may still go there with the Flycom. But I really, really like the Lightspeed when I fly alone. Very quiet and clear with the NR. I actually think I may have it worked out. When the passenger mike is disconnected, everything is quiet for both headsets, only when the passenger mike is on, that's when it's noisy. I have an additional inline push to talk switch, but I think it is wired via the ground to activate the mike through the radio (not my idea, someone elses) so it does not actually disconnect the mike. If I rewire it I should be able I think to turn on the mike through this switch, so the passenger can talk when they need to. I am going to try it. Otherwise I should be able to simply add an on/off switch to the mike jack, and the passenger can just turn it on to talk and then turn it off. If the mike is off the Lightspeeds are really quiet and comfortable, and having it on for brief periods while the passenger talks is not a problem.Sorry you are still having some issues.
Like I have said before trikes have solved this problem for a decade.
They either use Lynx which are uncomfortable and require batteries to charge every 20 hours of use in the helmet or my favorite Flycom set. It's not that uncomfortable. For a helmet system it's quite comfortable. More than Lynx helmet.
In open cockpit you can't use GA headsets, I have tried a dozen and failed with 5 different intercoms. Some kind of worked but kind of isn't good.
Once you fly the right solution a couple of weeks you will throw rock at Lught Speed Zulu and Bose and sigtronics and PS-Engineering coms and ATR built in com. They just kind of work. I decided to kind of stop using them many years back and just buy the last open cockpit helmet system I needed. Ian not trying to sell them, you can order direct but get the right solution once and you will more than likely never look back. Yes they are expensive but so is my hearing.