Poor readability

Hi,

I have a problem with my com system.
When my passenger has plugged in the headset the signal becomes very
weak.
I had the maintenance guys have a look at it but they say all works
fine.
We also use the same type of headsets and tried the mono/stereo
setting but this does not improve anything.
The intercom works ok.
At the moment I pull the plugs -so to speak- when I have to transmit.

Any sugestions
-Kees.