With mics, through line-in--not internal mics--I find my left channel a little hotter, at least according to the meter. But whether that is the mics, the battery box or the PCM-M10 is completely unknown. It could be happening anywhere in the chain, and it has nothing to do with internal mics.
Meanwhile, in playback, I don't hear it. This is probably one of those things that instruments can detect but humans needn't bother themselves about.