What was found
FLT 738 AIR RETURN, CLIMBING OUT AT 25K FT AND 320 KTS GOT SEVERE VIBRATION THROUGHOUT AIRFRAME. DISCONNECTED AUTO THROTTLES AND SLOWED AIRCRAFT TO 27 KTS, VIBES STOPPED. PERFORMED DETAILED VISUAL INSPECTION OF AIRFRAME IAW TSM 05-50 FOUND LOOSE FASTENERS ON PANEL 314AR (APU AREA). SECURED FASTENERS, NO OTHER DEFECTS. A/C OK TO CONTINUE SERVICE.