737 ACP
 

Can anyone explain to me why on some 737 airframes, with interphone selected on, the mic picks up lots of background noise to constantly annoy the other pilot while on other airframes it is nice and quiet? It doesn’t seem to have anything to do with the headset being used as even when you swap it for the observers headset or one of your own headsets it’s still the same. Is it a sensitivity setting within the audio control panel itself? Cheers