Terps and Orioles Fans: National Anthem Tradition?

There is a tradition at Terps Basketball games of shouting "ohhh" within the national anthem ("...that our flag was still there...(OHHHH!)...O say"). This is done by all of the student section, and many other fans. The same thing happens, to a lesser degree, at Redskins, Wizards, and Caps games. I was told, years ago, that this was actually started at Orioles games with the yelling of "Os." This makes sense, but it seems it would be easier for a student section (at Terps games) to organize and create the tradition. I can remember the tradition at Terps games, as far back as 20 yrs. Recently, I've heard more and more fans say you should not shout "Ohhh" at Redskins games, as this is a "Baltimore thing." (For thoses that don't know, University of Maryland is located just outside of DC and shares many fans with DC teams) Orioles fans were actually booed at RFK during the Orioles/Nats games for shouting it. Anybody know who actually started this and when?