Uncanny, as presented! Do you get this at all volume levels? Since U have switched speakers with identical results, it shouldn't come from the Sol's. Have U checked the right speaker's mid/tweaters' 1st reflection point vs the left? (but then, you've tried another room...) Anyway, if not, try dampening both reflection points identically -- try anything for starters (pillows... any absorbant matl).
Also, check out 1st reflection points on the ceiling. Finally, you may have one channel stronger than the other across the volume range -- or a phase inversion on one channel (unlikely).(but, again, you've tried other speakers).
Good luck!
Also, check out 1st reflection points on the ceiling. Finally, you may have one channel stronger than the other across the volume range -- or a phase inversion on one channel (unlikely).(but, again, you've tried other speakers).
Good luck!