2016 Lexus IS350 4 DR RWD

I AM THE ORIGINAL OWNER OF THE CAR AND AFTER 18,000 MILES, THERE IS SUSPENSION NOISE COMING FROM THE REAR PASSENGER SIDE. A LOUD THUMP CAN BE HEARD WHEN DRIVING OVER SPEED BUMPS, SMALL POTHOLES, OR UNEVEN ROADS AT MODERATE SPEEDS. DRIVING OVER THE ELEMENTS AT HIGHER SPEEDS, YOU CAN FEEL THE IMPACT THAT'S CAUSING THE THUMP. NO NOISE FROM SUSPENSION WHEN DRIVING THROUGH IT AT LOW SPEEDS WHEN DRIVING ALONE, HOWEVER, THUMPING SOUND IS PRESENT AT ALL SPEED LEVELS THROUGH EVERY BUMP ON THE ROAD WHEN I HAVE PASSENGERS IN THE BACK SEAT.

WHILE DRIVING DOWN ON I-90 WEST GOING TO BUFFALO NY COMING FROM BOSTON MA I ENCOUNTERED ANOTHER DRIVER IN THE LEFT LANE THAT WAS GOING EXTREMELY SLOW I TRIED TO ACCELERATE MY LEXUS EQUIPPED WITH PRE-COLLISION SYSTEM (PCS) AND THE VEHICLE STARTED BEEPING AT ME DETECTING THAT I WAS GOING PRETTY FAST ONTO THE PERSON IN FRONT OF ME, MY IDEA BEHIND DOING SUCH MANEUVER WAS TO PASS THE PERSON IN MY RIGHT HAND AND THEN GET OFF THE LEFT LANE OF THE HIGHWAY SO CAN GET OFF THE BACK OF THE SLOW PERSON, AFTER BEEPING SEVERAL TIME FOR SPLITS OF SECONDS I GOT TO GET OFF THE LEFT LANE SO THE PERSON ON MY RIGHT BECOMES THE PERSON BEHIND ME; THE CAR DID SOMETHING THAT IS NOT SAFE AT ALL AFTER ALL THIS AND ME NOT HAVING NOBODY IN FRONT OF THE CAR, MY VEHICLE CONTINUED TO BEEP AND APPLIED THE BRAKE PRETTY HARD ALMOST MAKING THE PERSON BEHIND ME CRASHING INTO MY BUMPER, I BELIEVE AS A CAR ENTHUSIAST THAT THE PCS ON THE LEXUS VEHICLES HAS TO BE IMPROVED AND REVISED SINCE IT HAS A HUGE LAG OF TIME REACTION , I CONSIDER THIS A BIG SAFETY ISSUE FOR OUR ROADS!