Can anybody help for listening playback from pstn line?


I have already assigned this problem but no one seems know about it.
I cannot hear playback or background IVR from cell or any landphone.
In CLI it is showing that they are playing perfectly.

My OS is FC11 asterisk 1.6 dahdi 3.5.5 at first trying zap which did some problem so use dahdi for my sangoma card and incoming pstn line working fine.

Some where i read if there is zaptel driver or sangoma it might happen.

But they said it can happen they did not said how to get out of it.

Can any one help to troubleshoot it?