Echo on calls

Asterisk server A makes a phone call to some random phone number via SIP through our provider. Once someone picks up the call (a human), the call is transferred via SIP again to Asterisk server B where there’s a queue and agents are logged in using eyeBeam/xLite.

Asterisk server B has agents logging in from two locations. First location is in the west coast US, the second location is in the Philippines. Asterisk A and B are located in east coast US.

The calls are being made to phone numbers of our customers.
US Agents complain of echos.
Philippines agents don’t complain of echos.

This is a pure VoIP setup, no TDM/PRI stuff at all.
How can I solve this?