When my truck is idling I will get this intermittent rattle from the drivers side under carriage. It is a deep roaring rattle that sounds like a loose heat shield or something like that.

Its something on the exhaust for sure.

I can apply pressure to almost any part of the exhaust system and the rattle goes away.

I have tried to tighten every connection to ever heat shield and part of the exhaust to NO avail.

Argh..

I don't know what else to do but take it to an exhaust shop. Any other ideas?

Kind of frustrated that I do my own oil changes but can't find a stupid loose something or other under the truck. Causing an owner who can't stand rattles to go crazy!

Thanks!

 

Could be a cracked Catalytic Converter core. They can make a lot of racket.

But don't give up too quick on heat shields yet. Many years ago I had a car that got a real rattle. All the converter heat shield bolts were tight and nothing looked broken or rusted apart. But I was convinced that one of them was rattling anyway. I took a piece of 14 or 12 gauge house wire, stripped off the insulation, and wrapped the wire tightly around the converter heat shields top and bottom. Twisted the wire ends together with a pliers to get it good and tight. It stopped the rattle on the converter. Closer look showed that the heat shield metal had cracked through next to a mounting bolt. I left the wire on that one, it never rattled again.
With a long converter, it might take 2 wires spaced out to cover the length.
It cost me zero dollars to troubleshoot and fix

 

I had a rattle or moaning type noise in my 00 F150 that turned out to be a combination of two different items.The transmission mount had collapsed and was allowing a vibration to transmit throughout the entire truck.There is also an exhaust support and bracket that has a rubber insulator in it that mounts with and directly above the transmission mount and has a single nut that attaches to the left side exhaust pipe.It was bad as well.Replaced both pieces and all is good in the world again...I dont know if your symptoms were the same as mine but I chased this problem for a couple of years...It was very intermittent and ambient temperature related---It was very WEIRD....

 

A lot of the cat's have heat shields that are just attached with bent over tabs. Sometimes you can crimp these tabs with diagonal cutters, or crush them tight with a C clamp. If in doubt on whether this might be the case, just start the truck, and using pliers, just get a good squeeze on some of these. The noise stops instantly.

Dave