I think some heckling actually adds to a debate, and I think sometimes when there's some mild heckling, it aids a debater, but when it gets out of hand, how do you control that?
I have no suggestions for you except that it could be the Speaker, and as was said earlier, the leadership has to set the tone. There has to be a school for proper heckling or something, some training. I don't have any magic rule changes to suggest.