Hallo,
we upgrated a OS 7200, change MGI to OAS, change MCP to MP20, install ver. 4.98 on MP20. After the upgrade we have clicking noise (every second) for outgoing calls on ISDN Trunk.
I had the same problem a few years ago, by exchanging the cabinet I could fix the problem. Is there another solution?

Are all the cards upgraded to the proper versions?

Does the clicking noise happen when you have default programming in it? I would suggest defaulting the system and trying it then. If it goes away then it was a corrupt DB. You may have to put in everything manually. Also, as John807 said, are all the cards upgraded to their latest versions?

Yes, all cards are upgraded , OAS and BRI.

Have you tried it with a clean defaulted database?