2012 TOYOTA AVALON Suspension Problems

I PURCHASED THE AVALON AT THE END OF THE 2012 YEAR. IT NOW HAS 16,000 MILES ON IT. THE CAR IS GARAGED OUTSIDE IN MASSACHUSETTS. ON NOVEMBER 10, 2012 (MONTH AFTER PURCHASE) AND YESTERDAY, JANUARY 28, 2014, THE CAR WAS BROUGHT BACK TO THE DEALERSHIP FOR A REAR SUSPENSION CLUNKING NOISE THAT HAPPENS DURING COLD WEATHER (32 TO -10 DEGREES FAHRENHEIT). BOTH TIMES THE MECHANICS SAY THEY CANNOT FIND ANYTHING WRONG, NOTHING IS LOSE WITH THE SUSPENSION, AND THERE ARE NO RECALLS ABOUT IT. THE BEST WAY TO DESCRIBE THE NOISE IS WHEN GOING OVER POT HOLES IN COLD WEATHER, I HEAR A CLUNK FROM REAR SUSPENSION (BOTH LEFT AND RIGHT SIDE) LIKE SOMETHING IS LOOSE IN THE TRUNK (TRUNK WAS COMPLETELY EMPTY YESTERDAY). THE SOUND IS NOT TOO LOUD, BUT AUDIBLE ENOUGH TO NOTICE. THE REAR STRUTS PERFORM WELL, AND THE CAR DOES NOT BOTTOM OUT. AS SOON AS...