It's been a while, but I don't recall any of of my instructors yelling at us for anything other than a good reason. A good reason, however, could be having to tell you twice how to do something. They never yelled at us jsut for the sake of yelling. Ultimately, they're there to teach you, not to enjoy a power trip, but they have only so much time and a lot of knoweldge to pass on. The faster you learn, and the faster you get your crap together, the faster they'll stop yelling. BMQ is a long 3 months (actually, I have no idea how long it is any more...), and after a while, even instructors get tired of yelling.