As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB-OUT FROM DTW, EXPERIENCED MEDIUM FREQUENCY AIRFRAME VIBRATION AT 310 KNOTS. LEVELED OFF AT FL230 AND REDUCED SPEED TO 290 KNOTS AND VIBRATION STOPPED. AIRCRAFT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE TROUBLESHOOTING REVEALED YELLOW HYDRAULIC SYSTEM ACCESS DOOR WITH SLIGHT AMOUNT OF LOOSENESS. REPOSITIONED LATCH, OPS CHECKED OK.