As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 4097 REPORTED THE APU VIBRATING THE WHOLE AIRCRAFT WITH AN ASSOCIATED BURNING SMELL IN THE AFT CABIN AREA. MAINTENANCE TROUBLESHOT SYSTEM AND FOUND THE AIR CYCLE MACHINE GRINDING. THE UNIT WAS REMOVED AND REPLACED AND THE SYSTEM OPERATIONAL CHECKED. ALL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.