Got a customer site where they want to use BGM on IP phones for right or for wrong and the levels change regularly.

They have the BGM on the key sets turned up fairly high on the key set volume control which is providing fairly low level BGM then an incoming trunk call comes in and the BGM goes really loud.

Haven't changed LIU as I figure it is system related / LIU was fine on old system with digital key sets.

System config

7200S 4.53
OAS / MGI
SMT 3105's and 5230's
PSTN trunks

Any ideas?