I think I need to explain the setup before the question will make any sense.

The scenario is:
Mitel SX-200 ML at a hotel with an incoming T1 from telco. Calls for Reservations are forwarded off site to a call center application via a LS trunk in the Mitel that connects to an Adtran 924. (FXS port in the Adtran) The Adtran uses SIP to connect to the remote Call Center. If the call needs to be rerouted back to this hotel, they return it via a specific channel of the Adtran which connects to a specific trunk in the Mitel that is DIL via Form 14 to a specific station/agent.

The problem:
It works surprisingly well except that the station/agent at the hotel that receives a call via this route is hearing some local echo/feedback in their handset. The original incoming caller does not hear any echo.

The Call Center techs are asking if I have any way to reduce the mic gain on these trunks/lines in the Mitel.

I'm at a loss with this one.
(pardon the pun)