As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON CLIMBOUT FROM DTW CONSTANT LEFT ENGINE N1 VIB INDICATION, AT NORMAL CRUISE POWER IN EXCESS OF 3.2. NORMAL INDICATION AT REDUCED LESS THAN 60 PERCENT POWER SETTINGS. EMERGENCY DECLARED, A/C RETURNED TO DTW LANDED SAFELY. PERFORMED INSPECTION OF LEFT ENGINE PER GE ENGINE MANUAL 72-00-00 FAULT ISOLATION 17 PROCEDURE 3B. OPS CHECKS GOOD.