As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ENGINE HAD LOW FREQUENCY VIBRATION AT POWER SETTINGS ABOVE 70 PERCENT N2. FLIGHT RETURNED TO DTW WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE PRBC AND TESTED THE ENGINE. ENGINE PERFORMANCE WAS SATISFACTORY. AIRCRAFT RETURNED TO SERVICE.