We upgraded from version 11 to 15 over the weekend and everything went smoothly with all extensions being recognized and the SIP trunk from Appia working well. This morning, the phones would work internally and we could accept calls but no audio could be heard on any external calls, whether dialing in or out. If someone got the auto-attendant, it was just a loud static. We restarted the 3CX services and all returned to normal for an hour. Then, it repeated itself and self corrected. This was never an issue prior and is intermittent, although problematic. Any thoughts? Suggestions?