Hello!
1. Do you use "Two Sound Mixing" option of Bandicam?
=> If you do, try only Primary Sound Device.
=> Do you still have the lag problem?
----- If you still have the problem -----
2. Do you use Windows 7/vista?
=> If you do, try "Stereo Mix" sound device in Primary Sound Device.
=> Do you still have the lag problem with the Stereo Mix device?