Has anyone had any problems with volume on the STS door boxes?

I have two installed at a site. When I press the door box button, the person answering the phone can hear me just fine, but I can hardly hear them. The volume slide is turned all the way up.

The really weird thing is: when a station direct dials the door box, it sounds great! It only sucks when you try to call from the door box to a station.

Here is what I have tried so far:

-have changed ports – no luck
have replace the boxes with new boxes – no luck
-have turned up the volume in WinDBA – no luck
-have plugged in a digital phone on the port and turned up the volume – no luck

Tech support says they can not replicated the problem.

Any thoughts???