As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE, WHOLE AIRCRAFT SHUDDERED AND VIBRATED MULTIPLE TIMES. (FLT 6345) PERFORMED GENERAL VISUAL INSPECTION OF AIRCRAFT INTERIOR, NO VISABLE DEFECTS NOTED. INFLIGHT TEST GOOD - FLEW FROM DEN -COS AT 300KTS AND NOTICED NO VIBRATING OR SHUDDERS.