Yes I know it's an antique
However...
Here's what's happening- Extension 10 gets called constantly from the VM and it only rings 1 time and you can see in the display Voice Messaging System.
I power cycled the VM
I did a reset save all on the Partner (ACS)
I called each vm port (4) and they all answer fine
I called 777 and the calls hit each port in a circular hunt
I checked to see if there were any system security or admin messages- none
I forwarded every station back to itself even the vm ports and ports they are not using
I changed the operator extension in system parameters to 11 and 11 started getting the calls
I moved x30 into the room where the system is and changed the oper extension to x30 and monitored the vm ports-every minute or so vm port 1 would go off hook and ring x30 1 time and hang up. It kept on happening with vm port 1 so I remover port 1 from the hunt group and unplugged it from the system.
It seemed to stop and I monitored it for a while longer.
It did not happed for 10 minutes so I put 10 back as the oper extension and left.
It started happening again so I remotely changed the oper ext. to an unused extension for now since the receptionist was going crazy with all the calls.
Any suggestions besides trashing it??

Did you make sure only the vm ports were programmed in #505.  If another extension is in there by accident that can cause it to bounce out to x10.

Is it possible that the message waiting light for one of the voicemail ports is turned on? The single line ports of the VM interpreted and ringing. The VM port answers, and not receiving mode codes, transfers the "call" to the CASO


See if there is a mailbox created on one of the VM port extensions.
 

do the same test but this time put vm station # 1 to  port 2  on the mail card

is this a 2 , 4 or 6 port  R3  ?

you may have a bad port card