asterisk users - Aug 2005 - Echo during begining of incoming calls

I am having a problem with echo during the begining of incoming phone calls 
on our TDM04B.  The echo is only noticable on our end and will eventually go 
away.  It is also noteworthy to mention that during the day incoming calls 
ring 3 phones first before going into an automated menu system.  If we 
answer the call immediately, the echo is present.  If we wait until the call 
goes through the menu system, enough time has elapsed that the echo is not a 
problem.  The problem doesn't occur when we dial out or when a call is 
connected through our VOIP provider.

I have tried modifing the gain, echo cancel, and echo training values 
without resolving the problem.  Everything I have read in the wiki and 
previous posts here suggest changing these values and testing will take care 
of the issue.  Any other suggestions on how to get this resolved?

Thanks
Ben