Stupid, I know, but are the physical controls on the side of the camera set correctly? I.E. volume dials are not at 0?
Under the Audio Input Settings, do you have Channel 1 and 2 mapped to Input 1 and 2? If it’s set to something else, then that might be the issue.
The Audio Input Level setting is another one to check–it’s a software setting different from the physical dial on the side of the camera. Also, the individual Channel Levels can be mapped to the global Audio Input Level or to the physical side dials–if they’re mapped to the global software Audio Input Level and not the side dials, that could be the issue.