I have an OLDER Rockwell RCC Three Cabinet system still on 7.1e. One of my Network shelves N-5-x seems to be giving me fits. Some of the Rockwell Consoles connecting to the BRL's on the shelf are experiencing a humming noise when you place an outbound call and on the inbound calls. it is not all of the consoles within that group. Could this be associated to the NSC or the TSI card? I have swapped BRL cards out without success. any suggestions would be helpful.