Rattling noise under truck

I've got a loud rattle coming from my truck. It's somewhere in the front of the truck or just beneath the passenger. I can't really tell. I thought it was a loose clamp on the exhaust that I found. I tightened it and the noise is still there. Any ideas?

 

get under the truck when its cool...........or use a rag around ur hand if its warm.

Smack the steel cage around the cat.... sometimes rocks lodge in there and rattle around and drive ya knuts

 

I have a rattling noise where my rear o2 sensor is. Pretty sure its falling apart in there.

 

wouldnt that throw a code?

 

It would, I replaced my o2 senser 2 months ago. The code throws "Air fuel ratio sensor" or something like that. I hit the metal around my cat earlier before I posted this. If I hit it hard enough I'd here some movement inside right after, but it didn't seem nearly loud enough to be what I keep hearing.

 

Yeah if it was the actual o2 sensor falling apart. But I think it's the hardware that rusted through. I haven't taken it apart yet to find out for sure.

 

Also check the heat shieldI(s) itself. Sometimes the heat shield starts to rot off and the shield rattles. And one other thing, I had a truck that developed a loose internal baffle in the Cat. I elected to live with the rattle until I traded in for my Taco. Can you borrow a mechanic's stethoscope???

 

I had the same thing, only more near the rear of the cab, almost pulled my diff apart but then found a peice of heat shield was rubbing on the drive shaft... Easy fixes ftw!

 

I have something similar but don't know what it is. Only rattles while in drive at idle. I got underneath it and it it seems to start/stop when i firmly press against the exhaust pipe past the rear o2 sensor. Nothing seems loose from what i can tell. Can't figure it out.

 

check your carrier bearing for excessive play. i had a high-pitched squeak/rattle that happened whenever i let off the gas. traced it to the carrier bearing.

 

This!

 

A Loose baffle plate in the Cat or Muffler?

 

Well I'm going to be checking my truck for all this when I get home...