Cisco T1 hwic echo

We use IP phones and we connect directly to our other office using a HWIC-1T  line on a cisco 1941 router.  On the one side the sound quality is perfect.  On the other side the sound has a echo.  Is there commands that I can do to eliminate. 

this is what I have

interface Serial0/0/0

ip address 10.1.100.1 255.255.255.0

service-module t1 clock source internal

service-module t1 timeslots 1-24

I am using a cisco 1941 with a hwic dsu/csu inteface card.

I know that, unlike the Cisco 2900 platform, the Cisco 1941 cannot be used as a Local Gateway Service (LGS) for a Hosted Voice Service (HVS).  However, I think you should be able to use it to support voice. 

A Cisco WS-X45-SUP7L-E   module supports up to 2M rate. The question is that, are you using this circuit for both voice and data? if the answer is yes, have you separated your voice traffic from your data traffic or do you let the two compete for bandwidth?

Voice has to be protected and there are two ways you can do this. On your LAN, you can have a dedicated VoIP subnet. You can then design QoS to protect that subnet in the event of congestion.   You need to do more tests to find out why voice works on one side but not the other.