Narrative:

This was an originator aircraft. We arrived at the gate and began our preflight duties. My first officer (first officer) did the walk around and returned and indicated the aircraft was in good shape. We completed our duties and checklists and called for pushback. I communicated with ground personnel and advised them that 'a pumps are off; door lights are out and brakes are released'. We had a normal pushback; taxi; and all checklists were completed including recall checks.after takeoff we both noticed a slight vibration. We discussed on climb out that it sounded like the main gear door was perhaps not completely closed. We got a clearance to climb to 17;000 ft; and when we were passing through 8500 ft I told the first officer that he needed to level off before 10;000 ft because I noticed we were not pressurizing. Due to our current climb rate my first officer climbed to 10;200 ft and we got the cabin altitude warning horn. We put our oxygen masks on and completed our immediate action items while descending back down to 9000 ft. ATC was notified and he assigned us a new altitude of 9;000 ft. We advised them of our pressurization problem and they wanted to know if we were declaring an emergency. I stated negative but we need a lower altitude and vectors back towards [the airport]. We completed the uncontrollable pressurization checklist but we could not control the cabin. We had no indications within the cockpit that anything was abnormal. We did not have any indications on the pressurization panel; no master cautions; or other lights. We then discussed the possibility of a rupture in the hull of the aircraft. I communicated with the flight attendants and they said there was a loud rumbling noise and vibration in the forward part of the cabin. After receiving that additional information and with no door lights illuminated we agreed we had a hole in the forward section of the aircraft.I made a PA to the passengers and told them that it would be necessary for us to return to [the airport]. I tried calling ops on the return but was unable to get them to answer. I ran the performance for an overweight landing and discussed with my first officer that if we had a hole in aircraft we should get the aircraft on the ground before any other damage could occur. He agreed and we elected to make an overweight landing on runway 23L. We had a normal approach until we lowered the landing gear. There was a noticeable vibration and the noise level in the cockpit was much louder than usual. On short final (below 500 ft) we got a master caution and an equipment door light. The landing was smooth and we rolled to the end and taxied [to the gate]. On the taxi in I had my first officer check with the F/as (flight attendant) on their condition and the condition of our passengers. They said everyone was fine and glad to be back on the ground as the vibration in the forward cabin was very noticeable. Upon arrival at the gate it was confirmed that the equipment door aft of the nose gear was open. It was also confirmed by maintenance that the associated door light in the cockpit was inoperative and would need to be deferred.

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Original NASA ASRS Text

Title: The flight crew of a B737 reported that during climb they heard a strange noise and were unable to pressurize the aircraft.

Narrative: This was an originator aircraft. We arrived at the gate and began our preflight duties. My F/O (First Officer) did the walk around and returned and indicated the aircraft was in good shape. We completed our duties and checklists and called for pushback. I communicated with Ground Personnel and advised them that 'A pumps are off; door lights are out and brakes are released'. We had a normal pushback; taxi; and all checklists were completed including recall checks.After takeoff we both noticed a slight vibration. We discussed on climb out that it sounded like the main gear door was perhaps not completely closed. We got a clearance to climb to 17;000 ft; and when we were passing through 8500 ft I told the F/O that he needed to level off before 10;000 ft because I noticed we were not pressurizing. Due to our current climb rate my F/O climbed to 10;200 ft and we got the Cabin Altitude Warning horn. We put our oxygen masks on and completed our immediate action items while descending back down to 9000 ft. ATC was notified and he assigned us a new altitude of 9;000 ft. We advised them of our pressurization problem and they wanted to know if we were declaring an emergency. I stated negative but we need a lower altitude and vectors back towards [the airport]. We completed the Uncontrollable Pressurization Checklist but we could not control the cabin. We had no indications within the cockpit that anything was abnormal. We did not have any indications on the pressurization panel; no Master Cautions; or other lights. We then discussed the possibility of a rupture in the hull of the aircraft. I communicated with the Flight Attendants and they said there was a loud rumbling noise and vibration in the forward part of the cabin. After receiving that additional information and with no door lights illuminated we agreed we had a hole in the forward section of the aircraft.I made a PA to the Passengers and told them that it would be necessary for us to return to [the airport]. I tried calling Ops on the return but was unable to get them to answer. I ran the performance for an overweight landing and discussed with my F/O that if we had a hole in aircraft we should get the aircraft on the Ground before any other damage could occur. He agreed and we elected to make an overweight landing on Runway 23L. We had a normal approach until we lowered the landing gear. There was a noticeable vibration and the noise level in the cockpit was much louder than usual. On short final (below 500 ft) we got a Master Caution and an Equipment Door light. The landing was smooth and we rolled to the end and taxied [to the gate]. On the taxi in I had my F/O check with the F/As (Flight Attendant) on their condition and the condition of our Passengers. They said everyone was fine and glad to be back on the Ground as the vibration in the forward cabin was very noticeable. Upon arrival at the gate it was confirmed that the equipment door aft of the nose gear was open. It was also confirmed by Maintenance that the associated door light in the cockpit was inoperative and would need to be deferred.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.