I have a 200EL in a hotel. I have two trunks on different cards in different bays with a loud chatter noise on the trunks. This only occurs if you make a call from the mitel side. The trunks are good from the telco side.

I've replaced LS/GS cards and changed the pair and the 25 pair cables and added more ferrite cores. I've even put the cards in a different bay. Same problem

I believe there is some sort of interference from a fire alarm cable but I can't find it.

Do you have any recommendations?