This phone is connected to an analog port. When this phone is on an internal call to an M or T series sets there is noise that makes it difficult to hear the conversation. External calls are OK. I have reviewed the B159 settings and made changes. I have also changed the ATA settings in the Nortstar MICS on the analog port. The two settings were connection type (internal or outside) and Phone set or Modem. None of the changes have made any difference.