B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 93
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
While at FL380 in cruise flight; the 'A' Flight Attendant advised us of some kind of noise he was hearing in the forward galley area of the aircraft. We looked at our pressurization panel and noticed that the cabin was around 9;000 feet and the vertical rate on the cabin was above 500 feet per minute. We had no indication on the Flight Deck that the cabin was indeed rising. We decided to put the packs in high mode while we reviewed the checklist. It took just a few seconds with the packs in high mode for the cabin to start coming back down and stabilizing. We decided to leave the packs in high mode until FL180 when we performed our descent checklist. The aircraft was taken out of service upon our arrival. Hopefully they can find out what the issue is with the pressurization system on this aircraft.
B737-700 Captain reported cabin climbed to 9;000 feet; so packs were put in high flow mode to control pressurization.