You stated the other phones have the hum also, but the two line phone is worse. Unplug the two line phone and see if the other phones still have the hum. I suspect the two line phone.
How about if you plug a SLT into the MJ hum or no hum?
Visit Atcom to get started with your new business VoIP phone system ASAP
Turn up is quick, painless, and can often be done same day.
Let us show you how to do VoIP right, resulting in crystal clear call quality and easy-to-use features that make everyone happy!
Proudly serving Canada from coast to coast.
