As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, NOTED NR 3 ENGINE VIBRATION ROSE TO 0.6 ABT 30 MIN INTO FLT VIB ROSE TO 1.1, RETURNED TO MSP. 20 MINUTES OUT OF MSP VIB WENT TO 1.2 RETARDING POWER LEVER KEPT IT BELOW 1.2, AUDIBLE SOUND HEARD AND VIBRATION FELT IN YOKE. MAINTENANCE REPLACED NR 3 ENGINE. ALL CHECKS GOOD.