Locating rattling sound??

MY sons 1999 s 10 blazer has a weird rattle to it. It is more on the passenger side of the blazer. When you first start it up it is quiet but after a few seconds it starts to rattle. Sound like a rock bouncing around the bottom of a can or something. I have gotten underneath and tried to listen, but can't pin point it directly. I am wondering, if it is the flywheel that is cracked will the sound always be there or come and go at times like it seems this does.

MY sons 1999 s 10 blazer has a weird rattle to it. It is more on the passenger side of the blazer. When you first start it up it is quiet but after a few seconds it starts to rattle. Sound like a rock bouncing around the bottom of a can or something. I have gotten underneath and tried to listen, but can't pin point it directly. I am wondering, if it is the flywheel that is cracked will the sound always be there or come and go at times like it seems this does.

Does it change when in gear or out of gear or speeding up engine?
Be sure to check heat shields on cats to.

Check the cat, mine was rattling before it got completely clogged

Catalytic converter. Very common issues on these trucks as well as the Astro vans

I have a muffler shop and those 95 to 99 converters are one of the most popular to go bad. You can thump on the muffler and listen for the rattle in the converter, wear a glove if its hot.