Sound bug on recording whith Blackmagic Intensity Shuttle

Hello,
I’m record conference (duration from 1h30 to 3h), for that :
For the picture I use BoinxTV with a Blackmagic Intensity Shuttle connected to a Sony Handycam.
For the sound I use Wireless microphone connected to the Macbook with a USB to Jack connector.
The computer is Macbook pro Retina 2,6ghz with NVIDIA GeForce GT 750M and 2 Go memory GDDR.

When I’m not recording, there no problem, no delay with the sound. But when I record the video, at the begining there is no problem. But after 25-30mn of recording, some crack and a big echo appear, sound begin to be inaudible during 30s and after sound become good again.

Do you have an idea where the problem come from ?

Please refer to this Article in our Knowledge base to fix this issue: http://boinx.com/connect/boinxtv/knowledge/recording/WS02864