Sound panning

When in cockpit or VC view, and I flick the view from side to side I hear the engine sound move from one side to the other with default and addon aircraft. In my aircraft the sound stays centered. How do I get the panning effect. What I have noticed is this. My stereo sounds are louder for the channel relating to the engine on that side. That is, the right channel is louder for the right engine and vise versa. Other planes that use stereo sounds, and have ban and bbn files (for left and right engines) are the same volume for each channel. I wonder if this is the reason?Thanks,Nick.