I had a sound that I couldn't figure out for quite a while and it turned out to be that the top center bolt for the fan shroud fell out (months before) and found it's way to a place where it was rubbing on a pulley. At idle, it was quite noticeable, but higher rpms it got drowned out. See if your shroud bolts are all present. Just a WAG.

 

I've seen a lot of them with a broken bracket by the passenger side exhaust manifold where it ties into the downpipe. Usually a little welding fixes them right up. You should be able to look in the passenger side wheel well and check it out. Just a guess:thumb:

 

My 06 had that noise and i found a broken down pipe when replacing it i found leaking bellows on EGR up pipe . Replaced manifolds up pipes and down with PPE stuff and noise is gone. I think the leaking up pipe made the buzzing sound sound that would come and go just like you described. I am guessing that my blocker plate added pressure to those bellows and helped them to fail.

 

Funny, I have the EGR blocker plate in as well and have had it in since 2010ish. Might have to do some dick traceying in that area now. Thanks,

 

Good info. My truck also has this noise. Can't figure it out.

 

If you can get in there and look at the up pipe passenger side that feeds the EGR that bellows is where you will find black soot . Thats your leak and it buzzes like a heat shield that's loose . Now that i think about it you cant see it until the down pipe is removed . This is the time that you tell your wife that all the pipes are bad and need replaced just like when you put in a new water heater you need all new lines.

 

So I found the rattle. It was the damn turbo heat shield. It was missing one of the 3 bolts that holds it down. I had my wife get in the truck while I climbed up in the engine bay. Then I had her slowly rev until it hit the vibe frequency. I then started crabbing anything any everything trying to find it. Put my hand on the turbo heat shield and started pushing down and it stopped. That's when I noticed the damn bolt was missing. Thanks for the help fellas!! I still might tell the wife that I need a new down pipe. ;-)

 

That's just one of the many I have found, I have one between the A-pillar and DRL sensor on the drivers side just below the dash panel that comes and goes with the weather... :think:

There is another potential one (fixed mine already), the heat shield that protects the large connector at the passenger rear of the transmission.....