I've got a PA400, similar, but 4 place. It's pretty quiet.
Try the unit at home where aircraft electrical interference and wind noise aren't going to be a problem.
Have you got a decent mic muff?
Try it with different headsets.
The only headsets I've had compatibility problems with (in other aircraft intercom systems) are DC's. I've got a PA21-60, a basic
Harry's and a no name, and all are fine.
Squawking 7700