Narrative:

Upon takeoff from ZZZ; we immediately received an amber APU fault and APU low pressure indication on the EICAS. At the same time; we noticed a loud sound coming from the forward right side of the aircraft. The noise was louder and more pronounced than a gpu or intercom door being left open. It sounded like the air driven generator had deployed and was running. I shut down the APU on the climb out. After cleaning up the aircraft I checked the electrical synoptic page and the air driven generator was not shown pwring the essential bus. Upon the climb out we also received the 'stall fail' amber message. I made the decision to return to ZZZ. I did not declare an emergency but did have the trucks standing by due to the uncertainty of the noise up front. The flight attendant; maintenance; ATC and the passenger were notified. We leveled off at 4000 ft and proceeded with a right pattern back to runway. I assumed control of the aircraft on base after all parties were notified and we were ready to land. Landed without incident; taxied to gate and notified ATC that the emergency trucks were no longer needed. I chose to de-board the aircraft being we had not restarted the APU and the right engine was still running; powering the aircraft. Upon inspection; the oxygen door was open and no other signs of abnormality were observed.

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Original NASA ASRS Text

Title: LOUD EXTERNAL AIR NOISES AND INAPPROPRIATE EICAS MSGS ALERT CRJ FLT CREW. AFTER LNDG; NOISES ARE TRACED TO AN O2 SERVICE DOOR LEFT OPEN BY GND CREW. FLT RETURNED TO DEP ARPT FOR MAINT.

Narrative: UPON TKOF FROM ZZZ; WE IMMEDIATELY RECEIVED AN AMBER APU FAULT AND APU LOW PRESSURE INDICATION ON THE EICAS. AT THE SAME TIME; WE NOTICED A LOUD SOUND COMING FROM THE FORWARD R SIDE OF THE ACFT. THE NOISE WAS LOUDER AND MORE PRONOUNCED THAN A GPU OR INTERCOM DOOR BEING LEFT OPEN. IT SOUNDED LIKE THE ADG HAD DEPLOYED AND WAS RUNNING. I SHUT DOWN THE APU ON THE CLBOUT. AFTER CLEANING UP THE ACFT I CHKED THE ELECTRICAL SYNOPTIC PAGE AND THE ADG WAS NOT SHOWN PWRING THE ESSENTIAL BUS. UPON THE CLBOUT WE ALSO RECEIVED THE 'STALL FAIL' AMBER MESSAGE. I MADE THE DECISION TO RETURN TO ZZZ. I DID NOT DECLARE AN EMER BUT DID HAVE THE TRUCKS STANDING BY DUE TO THE UNCERTAINTY OF THE NOISE UP FRONT. THE FLT ATTENDANT; MAINT; ATC AND THE PAX WERE NOTIFIED. WE LEVELED OFF AT 4000 FT AND PROCEEDED WITH A R PATTERN BACK TO RWY. I ASSUMED CTL OF THE ACFT ON BASE AFTER ALL PARTIES WERE NOTIFIED AND WE WERE READY TO LAND. LANDED WITHOUT INCIDENT; TAXIED TO GATE AND NOTIFIED ATC THAT THE EMER TRUCKS WERE NO LONGER NEEDED. I CHOSE TO DE-BOARD THE ACFT BEING WE HAD NOT RESTARTED THE APU AND THE R ENG WAS STILL RUNNING; POWERING THE ACFT. UPON INSPECTION; THE OXYGEN DOOR WAS OPEN AND NO OTHER SIGNS OF ABNORMALITY WERE OBSERVED.

Data retrieved from NASA's ASRS site as of May 2009 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.