VOIP One Way Audio over Ipsec

We have an Ipsec tunnel between site A (100D) and site B (60C).  We allow all services through both sites.  Whomever initiates the call can hear the user at the other end, but is unable to be heard.  I have already disabled and deleted the SIP helper at both sites and rebooted the firewalls with the same outcome.  What other things can be done to resolve and troubleshoot this issue?