I have a 2013 azera that rattles a cold start and after it sets for about 30 min. I know this is a problem with the 3.3 engines. Has anyone replaced the tensioner and how hard of a job is it.

 

There is nothing like doing part of the job today , part of it next week and maybe the remaining part next month.
If you are considering replacing the tensioner, do the whole job ONCE. replace the chain , tensioner , oil, filter and any related parts while in there.