We are experiencing intermittent "bursty" echo in a VoIP trunking application (digital phones behind PBXs). Callers experience the echo when connecting to the PSTN via remote PRI circuit (PRIs are connected to remote PBX). We have echo cancellation turned on in the PBX gateways and it doesn't appear to be a delay or latency issue with the network. Since by definition the echo should not becoming from the PRI at the tail end and latency doesn't appear to be the problem I think I'm left looking at a volume or loudness issue? As a side note, we don't get the echo on station to station (intercom) calls between the same sites (remote and sites with PRIs) which would utilize the same gateways, network connections, etc. Any tips or feedback would be appreciated. Thanks.