First 4 extensions on ix-psub card "screech" on co lines. Last 4 are ok. Other cards (i.e. 408) are ok and can access co lines. Already swapped out card and same problem. Any ideas? Great forum!

Check Class 10, Item 70.6 - Group Monitor- for the affected stations and disable it.

Thanks for the quick response, JBean. Tried your idea, but no joy. Just to clarify, the noise comes from the handset, and sounds like you've connected to an active fax machine. Unable to use any co lines.

What model phones are you using, and what software/system type?

If swapping cards didn't fix your problem, it's either a programming issue, bad wiring to the block or, although rare, a problem with the back plane. If you have the room, try moving the card to another slot. It's a real pain in programming, but it might fix your problem.

Adix APS, ver. 6.31 KT24 phones Card is in expansion module.

Just for the sake of thoroughness, verify the key patterns for the phones in question. Are you really accessing the CO line you think you are?