Red Sox Dugout Drumming?

Watching the past few games, the whole Sox dugout would randomly start (for lack of a better word) drumming along with the PA system. There was JD Drew rattling two water bottles together, Papi was smacking the roof of the dugout... All the guys were getting really into it. And, they did it more than once! I guess my question is, what in the heck are they doing, and where can I find a video clip of it? It makes me laugh, I mean, we all know they're a bunch of endearing idiots, but this is just another fun and crazy thing that tells us that these guys really *love* what they do, you know?