What was found
FLT 3090 - ON CLIMB-OUT FROM MSP, THE CREW NOTED AN AERODYNAMIC BUFFETING EVERY 5 SECONDS IN AIRSPEED RANGES BETWEEN 160-230 KNOTS. THE AIRCRAFT RETURNED TO MSP. MAINTENANCE PERFORMED TROUBLESHOOTING TO THE HYDRAULIC SYSTEM, FLIGHT CONTROL CABLE TENSION. ALL CHECKS GOOD. THE HYDRAULIC ACCUMULATRO PRESSURE WAS SERVICED AFTER IT WAS FOUND TO BE LOW. ENGINE AND DE-ICE SYSTEM CHECKS WERE ALSO PERFORMED. ALL CHECKS SATISFACTORY. (M)