A beep only the other party hears during the conversation

We are using Asterisk 1.2.24/FreePBX 2.2.3. For some reason there is a beep only the other party hears during the conversation. We don’t hear the beep in our side instead some of the words get cut-off during the conversation while the other party hears a beep.
We checked all the hardware and everything is checked out good. The VoIP has its own T1 PRI line and not sharing the data line. Can anyone help me figure out or point me to the right direction. We need to fix soon

Thank you in advance