I will have to listen again tonight. My memory is Angel hears an alarm and exits the guard room.
Michael hears the alarm and leaves the "computer room"
Michael gets to the stairway. I think it is a cement structure with metal stairs. SO, lots of echoes.

Michael sees Angel down a flight or two of stairs. Angel says "Comon" then we hear more metal stairs.

If Micahel is on Burts floor and Angel is on his way, why would Angel say comon? If Michael was on the same floor as Burt's armory, and was told the alarm was for Burts armory would he wait for backup (thus the delay and more stair sounds) or would he run right to Burt's? In any case, there is a squabble at the lock with Angel arriving first, but then hesitating and not unlocking it.