how does a downpipe or exhaust pipe for 2013 Malibu eco come apart at 65,000 mile

What is your question?

had tensioner and tensioner belt replaced. Immediately afterwards, as soon as driving off the lot, there was a twanging noise! I would say metal noise, vibration sound when accelerating intermittently. The shop forum called it a buzzing noise. They diagnosed the noise to be a cracking down pipe from exhaust manifold. They replaced the down pipe, exhaust pipe,the twanging noise or buzzing noise is still present. Take note, the noise was NOT PRESANT BEFORE THE WORK WAS DONE TO THE TENSINOR AND TENSINOR BELT. ONLY AFTER THE REPLACEMENT. Any help and or feed back would be greatly appreciated. The work has all been done in house, Chevy dealership, from day one of 2013. Thanks

What makes this problem better or worse?

NOTHING

How long has your 2013 Chevrolet Malibu had this problem?

SINCE WORK WAS DONE TO THE TENSINOR AND TENSINOR BELT 1-2 MONTHS