BCT expansion pack 2 demo

[Shorty]

Have just finished ep2 - this time winning I just wanted to know if I am the only one having BIG troubles destroying the northern most fire team in OBJ Lee? Waisted 3-4 fire teams assaulting + numerous fire missions. Finally getting rid of it by chance with an UH60 passing by?
Later I destroyed three enemy batteries, also by UH60s Seems a bit unlikely to me?
In start of the game I had drum rolls from time to time - anyone who can tell what that indicated?
Have purchased ATF - many hours of combat ahead