As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3937 SHORTLY AFTER TAKEOFF THE CREW HEARD A LOUD WHINE AND EXPERIENCED A VIBRATION FOLLOWED BY A HOT SMELL COMING FROM THE NR1 PACK. THE CREW SHUT THE NR 1 PACK OFF AND RETURNED TO ORD. THE AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED THE AIR CYCLE MACHINE IAW EMB 145 AMM 21-51-03. AIRCRAFT RETURNED TO SERVICE.