The Volokh Conspiracy
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Campus Reform (Celine Ryan) has the details, with video and with a statement from the university acknowledging that this happened:
Due to the nature of the event advocating gun rights, a Campus Public Safety officer monitored the event to ensure the safety of participants. When an individual disrupted the event by ringing a cowbell, the officer used his professional judgment and determined not to threaten or restrain the individual so as not to escalate a potentially unsafe situation. After the disruption, the meeting continued, and PSU facilities management allowed College Republicans to extend their meeting beyond the scheduled end time that night because of the disruption delay.
The event "continued" but only after over an hour of delay, according to the Campus Reform story.
UPDATE: I originally used the generic "shouted down" in the headline, but I decided to change it to "shouted (and cowbelled) down," partly to be more precise, and partly because I like the phrase "cowbelled down."