CLose to 1 year ago I replaced the drivers side cat on my 06 f150 w/110k miles and 2 weeks ago I replaced the passenger side cat and 02sensor. Now I'm hearing a metal on metal vibration noise but it's only under acceleration, when I let off the gas pedal I don't hear. It's definately underneath near the middle or maybe towards the front end of my truck. Could the driver side cat being going out again so soon ? A misfire was the cause of the passenger cat and I did a full maintenance job to correct that from COPs, plugs, fuel filter, FPDM. Fuel Additive, etc

 

Even if you replaced the CAT with aftermarket it shouldn't rattle with a year unless you put over 50K miles

I would crawl under and check all the hangers and heat shields and worse case could be your engine and trannny mounts.

 

Take a look at the heat shields surrounding the cats. They bend easy and could be touching.

 

I did see some suet on the passenger side of the motor, I was looking on top of the tire trying to see the exhaust manifold but the suet was right above that, around a bolt for the engine manifold

 

im not a mechanic so I hope someone can understand what I'm describing

 

Neither do I! But, still can't decipher what you are saying.

 

It may be a leak, I'm gonna bring it to my muffler guy tomorrow and find out what's going on because the sound is annoying.