Might be hard to tell, but does the sound seem to follow the engine RPM, or the drive shaft RPM?

This is an interesting problem.

 

Definitely the Engine RPM. the drive shaft doesn't move when im hard on the brake and reving the engine. So its definitely a noise coming from the engine compartment.

 

Exhaust system? Heatshield on catalytic convertor?

 

I had thoughts about the exhaust system too. How would you know if it was the broken cat syndrom?

 

I just use a hammer and tap around the entire exhaust system and listen for vibration. It could even be simply rocks stuck in the heat shield.

 

Mine is actually at higher speeds like 40+, and it is only when I step on the gas. when I let off the throttle the sound will go away but I will still be coasting at 40+ It is noticeable in the cab even with radio and conversation

 

Country: Yea, that is the same exact problem i have.

 

Dirty,
how long have you experienced this problem?

 

Since ive owned the truck...about 5 years

 

Yep mine has done it for the life of my truck too, about 2.5 yrs.

 

I dont know if the original poster got his answer, but check out the other post above about exhaust noise. FTJohnson had a great idea and there is a TSB attached. I believe it solved a long term metal rattle in my 2003 4.2L.

Remove the engine lift brackets.

Good luck
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