VIBRATIONS AND A LOUD SOUND FROM THE SIDE OF A BELL 206 CREATE THE NEED FOR THE PLT TO PERFORM A FLT CTL CHK PRIOR TO CONTINUING THE LNDG AT A HOSPITAL.

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ACFT; A BELL 206L; WAS FLYING A HOSPITAL-TO-HOSPITAL PATIENT XFER MEDICAL EVAC FLT. THE ACFT WAS IN THE CLASS B AIRSPACE UNDER RADAR CTL AT APPROX 2000 FT MSL PREPARING FOR LNDG AT ZZZ HOSPITAL. THE ACFT STARTED A 1-TO-1 LATERAL VIBRATION AND THE PIC IMMEDIATELY INITIATED AN INFLT FLT CTLS CHK TO ASSESS THE CONTINUED 'FLY ABILITY' OF THE ACFT. AFTER COMPLETION OF THE FLT CTLS CHK AND A SCAN OF ALL FLT INSTS IT WAS DETERMINED THAT THE PLT HAD FULL COMMAND AUTH IN ALL AXIS OF FLT. THE PIC MADE THE DECISION TO CONTINUE HIS APCH TO THE HOSPITAL HELIPAD. SHORTLY AFTER THIS TRANSPIRED THE MEDICAL CREW IN THE REAR CABIN AREA RPTED A 'LOUD POP' AND AT THIS TIME THERE WAS AN IMMEDIATE REASSESSMENT OF ACFT CTLS AND INSTS. THE RESULTS BEING FULL COMMAND AUTH IN ALL FLT AXIS AND NORMAL INST INDICATIONS BUT THE LOSS OF THE LATERAL 1-TO-1 VIBRATIONS. LNDG WAS COMPLETED TO THE HOSPITAL HELIPAD WITHOUT ANY FURTHER INCIDENT. UPON LNDG AND THE EXIT OF THE MEDICAL CREW FROM THE REAR CABIN AREA; THEY NOTIFIED THE PLT THAT THE L SIDE DOOR OF THE ENG COWLING WAS NO LONGER ATTACHED TO THE ACFT. THE PIC COMPLETED A POSTFLT INSPECTION FOR ANY FURTHER DAMAGE. THE RESULT OF THE POSTFLT INSPECTION WAS ONLY 2 SCRATCHES IN THE ACFT'S PAINT JOB.