Noise

yes, the heat shield rattles~

beat it with a ball-peen hammer or remove it to stop the rattling~

as far as it's seemingly random nature, one only needs to look at the expansion and contraction of metals over temperature to find out why this may have happened~

Interesting is that it can happen seconds after I start to back it out of the garage after sitting all night long or 20 mins into a drive. It is crazy...we drove it about 20 mins to the repair shop this morning, the darn car would not make a noise...we drove around in it with the mechanic...nothing..then on the way home, the noise and the best way I can describe it is like a chain dragging...tinkling sound not overly loud but for sure loud enough I can hear and I think others as they walk along.

My 2003 Highlander was making a similar noise, very annoying! My mechanic found gravel trapped under heat shield which is located under catalytic converter. He got some rocks out but there are still a few there.

My 08 highlander does the same annoying rattle - I was told it's coming from the double-walled exhaust pipe off the engine. The genius japanese cheap ass engineers created a pipe within a pipe to eliminate noise and the inside pipe is rattling. Very costly to repair as the entire pipe has to be replaced.