Can students legally drown out a speaker with whom they disagree?

No, the right to free speech does not include the right to disrupt the speech of others. “Otherwise there would always be a heckler’s veto,” said Erwin Chemerinsky, constitutional law scholar and dean of UC Berkeley School of Law. “The only speech then we would ever hear is that which is sufficiently noncontroversial that no one wants to stop it,” he added.

More here.

UPDATE: After the recent and disturbing events at CUNY Law, this post in In a Crowded Theater is quite apropos and on-point.