Hi guys just bought my truck last November, and up until now its been great. I was driving one day and it started making a rattling noise when it was in park or when it shifted (automatic) its almost like a rock in a tin can but much more suttle and deeper in pitch. I changed the starter a couple of weeks ago so I thought it might be a loose bolt, but I checked and all are tight. Nothing harming the truck (yet) just really annoying and i cant seem to find the noise, it is how ever coming from the engine bay, because i can hear it faintly in the cab, and more so behind the left tire. Got any ideas guy???

Thanks

 

try checking the idler pully, between the alternator and ac pump. If the bearings are shot in that pully it will make that noise.

 

Also, since it makes the noise in park.... (i.e., sitting still.....) start it up, and start crawling around under the truck, and see if you can isolate where it is coming from.

 

are you sure its not spark knock/pinging ?

check the auto trans shifter linkage. where the up/down rod transitions to the front/rear rod, there are nylon bushings at the end of the shaft. you can replace them, or just grease them heavily.

check the cat. when the internal stuff breaks loose, it can rattle.

 

thanks guys, ill check it out

 

It might be your torque converter? I've had this happen to one of my trucks with similar symptoms. It took the third mechanic to find it though.

 

catalytic converter or heat shield?

 

I'm gonna go with what seabass said and say your cat is on it's way out. Mine made this very noise in park a few years ago. Started my truck one morning and I couldn't hear my exhaust anymore and she wouldn't shift out of first. Had it replaced and the noise was gone. My guess is that something broke off inside the cat and was knocking around.

 

+1 on the cat. It'll vary from a high pitched chirp to the sound of a rock in a can like you described. I'd get underneath there and bang on the cat and see if it rattles. When cold, of course.