3com commercial modem chassis question
I work for an ISP and we have some 14 year old 3com USR modem chassis that have several modem cards in them. At one of our POP's on 11/25 there was a power surge in the area that took out one of the power supplies for that chassis. We replaced that and the unit powered back up but then customers had issues connecting. We then swapped out the card that had been connected with a spare in the same chassis. People could connect again but last night issues re-arose. When we try connecting from the office the times it doesn't connect; which is about 90% you can clearly hear a clicking sound almost like a static intermingled with the modem negotiating sound. Windtream had checked the PRI circuit that goes to that and can find no errors. My question is this; could something else in the chassis itself such as the replacement card or another component be causing that clicking sound and the connection issues or would that have to come from the PRI lines?