I love the title for this one, because you automatically think "... too quiet ..." :)

When you deactivate the door, you have to head back to the first building. There are now 2 invisible guys blocking your exit from this area, either run past them or fight them. Once out, head back the way you came in to get back to your 2 warthog buddies.

Enemies have reappeared in various places so be careful. Head forward - it's a small island and you'll loop around to where you began. You'll pass some medical supplies and rocket launchers along the way, which will be greatly helpful :). There are definitely new guards in front of the first building, so you'll need the warthog firepower and perhaps those rocket launchers to get through them. Save the rockets for later though, if you can. They're great at taking out the bigger guys in two hits.

This section ends when you get back in that door that was blocked before. Master Halo Walkthrough