Narrative:

On climb out at approximately 7;000 feet we heard a loud impact sound on the left forward fuselage. The first officer (first officer) stated she briefly saw a large white object pass by so we suspected a bird strike. Initially; all flight instrument indications and system parameters (engines; flight controls; pressurization; hydraulics; electrical; radar) appeared normal. During our assessment and after a few minutes the #1 flight attendant called and stated that she and the #3 flight attendant were hearing a strange sound coming from the left engine and felt a strong vibration in the floor of the aircraft. While on the interphone the first officer and I also felt the vibration and briefly saw the left engine vibration indicator (N3) jump. We then requested from ATC a turn back. We sent a free text message to dispatch and a radio call to operations informing them of the situation and briefed the flight attendants of our intent. We made the appropriate PA's. We then switched control of the aircraft to captain flying and accomplished the overweight landing and emergency landing checklist. Pulling off the taxi way we had aircraft rescue firefighting (arff) inspect the landing gear for overheating and the left engine for damage or leaks. After satisfactory inspection we proceeded to the gate without further incident.

Related reports:

Google
 

Original NASA ASRS Text

Title: B757 flight crew reports a loud impact on the left radome; from a large bird at 7;000 feet. Initially no anomalies are detected but then the flight attendants report a strange sound and a strong vibration coming from the left engine. The crew also feels the vibration and elects to return to the departure airport.

Narrative: On climb out at approximately 7;000 feet we heard a loud impact sound on the left forward fuselage. The First Officer (FO) stated she briefly saw a large white object pass by so we suspected a bird strike. Initially; all flight instrument indications and system parameters (engines; flight controls; pressurization; hydraulics; electrical; radar) appeared normal. During our assessment and after a few minutes the #1 flight attendant called and stated that she and the #3 flight attendant were hearing a strange sound coming from the left engine and felt a strong vibration in the floor of the aircraft. While on the interphone the FO and I also felt the vibration and briefly saw the left engine vibration indicator (N3) jump. We then requested from ATC a turn back. We sent a free text message to dispatch and a radio call to operations informing them of the situation and briefed the flight attendants of our intent. We made the appropriate PA's. We then switched control of the aircraft to Captain Flying and accomplished the Overweight Landing and Emergency Landing checklist. Pulling off the taxi way we had Aircraft Rescue Firefighting (ARFF) inspect the landing gear for overheating and the left engine for damage or leaks. After satisfactory inspection we proceeded to the gate without further incident.

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.