To drain the line, just unscrew the RCA plug on the interconnect that attaches to the sub, and pour the electrons out into a cup. Then you teach them the words so they don't have to hum ;~)
But seriously now... You've eliminated the IC as a cause of the problem. If there is another sub on the same system and it does not hum, but is connected in the same way (make sure AC power is same),then its likely that the sub is the problem. Try putting the IC from the good sub on the humming one and if it still hums, then its even more likely that its the sub. Can you swap it into another system?
But seriously now... You've eliminated the IC as a cause of the problem. If there is another sub on the same system and it does not hum, but is connected in the same way (make sure AC power is same),then its likely that the sub is the problem. Try putting the IC from the good sub on the humming one and if it still hums, then its even more likely that its the sub. Can you swap it into another system?