To check balance in left and right channels, look up Pulse Ultra - Build Your Cages. A stereo pan from left to right.
You may have to open them up (the enclosure) remove some screws and check to see if a wire is loose on the backside of the driver unit. If so, it will mess up proper polarity + and - , like on speakers.
Resoldering or even applying some silicone glue can solve the problem.