Mitel changed a component in the 8528 / 8568 phones, so you may find on some 3.2 systems and on some version 4 systems that this happens when you add newer phones to the system. Mitel fixed this with a new release of software for the phones that won't exist in your system.
You need to either 1) upgrade the system, or 2) get the new firmware file for the phones loaded in place of the existing file. When the phone is unplugged and plugged in again it will download the file.

We found as a temporary fix, that you can turn the vlume all the way up to the top on the handset and then back down again and the problem goes for a while.


Answer The Phones
Telephone Engineer
UK