Thanks for posting. I would first recommend that you upgrade the unit to latest Extended Maintenance Release (EMR) which is currently R11.4.3. Regarding the cause code 47 above, this indicates that the unit received a message that there was no resource for the call, but the reasoning was unspecified. We would typically want to check the output of the following so we can see more details.
debug sip stack message
debug voice verbose
debug isdn L2-formatted
However, with that type of error, I would typically expect the call not to come up at all, rather than a one-way audio condition. If you continue to have problems on the newer firmware feel free to respond here with the complete debug output minus any customer specific information such as passwords, phone numbers, or IP addresses.