I'm a ShoreTel technician working with a Mitel tech to connect ShoreTel to Mitel via a T1 Tie Line. We've tried various protocal configurations and have, for the moment, settled on NI-2 with ShoreTel as the Master. Calls are completed each way over the Tie Line; however we get overwelmingly high db noise during the ring secquence and throughout a call. ShoreTel engineers say it is a layer 2 (hardware) issue so I replaced ShoreTel T1 and the shielded T1 cross-over cable; and I grounded the ShoreTel T1 to rack. ShoreTel connects to the Mitel SX2000 via a 'Mitel MSU' then fiber to the Mitel SX2000.

Any ideas on the cause of the noise and how I can clear it?

Thanks.