Flight Crew Last 90 Days 299; Flight Crew Type 6000
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
Within approximately three minutes of level off at cruise altitude of FL400; we heard three to four loud thumps and the cabin began climbing between 400 to 500 FPM. The flight attendants were called and they verified that they heard the noise. They also noted that the cabin was louder than normal especially near Row 5 on the First Officer's side. As we begin to communicate with ATC for a descent; the cabin altitude had climbed to 9;000 FT. We began an ATC coordinated immediate descent for lower. This action preempted an altitude warning and potential emergency descent. As we began our descent the cabin began to climb at a higher rate; approximately 900 FPM. At about 9;500 FT cabin altitude; the cabin began to descend. The cabin stabilized [as the aircraft reached] approximately FL240. The pilot flying reviewed appropriate QRH checklists while the pilot monitoring coordinated with all appropriate outside agencies for the alternate. We diverted and landed without further incident.
B737-700 First Officer reports several loud thumps after leveling off at FL400 and the cabin altitude begins climbing. A descent is initiated and the cabin stabilizes as the aircraft reaches FL240. The crew elects to divert to a suitable airport.