2007 F150,4.2V6,16K miles
Another problem has risen on my truck;upon start up and until it warms up the passenger side catalytic converter is making a "loose rivet" rattling sound.It sounds like someone is shaking a tin can with a BB in it.I will be bringing it to the dealer this next weekend but am wanting to know if anyone else has had this problem too.

 

i had this problem on my mercury grand marquis, you could only hear sometimes, mostly could, but for me it was just teh shield, i just took it off and through it away...

 

Check for rocks and gravel in between the cat and heat shield. I have had to remove some a couple of times.

 

It is only doing it upon start up to operating temperature.Do rocks or gravel stop making noise when they heat up?

 

I had the same problem with both of my 97S. The spot welds that hold on the part number tag broke and it would rattle until it heated up. I split the heat shield and was able to yank out the tag and problem solved. I would not expect that with newer trucks.

 

It is only doing it upon start up to operating temperature.Do rocks or gravel stop making noise when they heat up?

Yea, once the rock heats up it expands and fills the gap and stops rattling !!

 

I am just saying, I had the same problem, and I had gravel in there, once I cleaned, problem solved, it is worth a look anyway.

 

I checked the Periodic Table,and the molecular structure of rocks and gravel are too small to expand that much under those heat conditions!

 

How about this... the cat heats up and expands outward enough to push the loose rocks into the heatshield. This is what mine was doing, so it does happen, maybe not your problem, but it can happen.

 

I finally crawled under my truck to check the rattle.After banging on it a few times with my hand I narrowed the rattle down to the rear of the heat shield,passengers side.I ran my hand over the top inside of the shield but could not feel anything.Finally,after 10 minutes of frustration,I hit up on the bottom of the shield and out popped a rock a little bit smaller then a dime!

 

Maybe the periodic chart was off a little LOL....J/K Glad you found the problem. It's always nice when it is something easy....