LOUD rattle when engine starts

[yevgenievich]

Really sounds like the exhaust pipe connection to the the egr

 

[GoToGuy]

I had similar sound, when we took the serpentine belt off started it no sound. Was either idler pulley or tensioner pulley. A bearing was going bad. That was us, yours sounds like it cycles rattles fast for low or idle rpm. Have you tryed a stethoscope on parts to trace noise. You've felt for rattle vibration on any parts attached to or have pulleys bearings on them? Don't loose fingers! Good luck.

 

[Frank Enstein]

Flexplate loose? Does it quiet down in gear?

 

[BOOT]

Another vote for sounds exhaust leak related.

 

[OrgasmicLarry69]

Another vote for sounds exhaust leak related.

It very well could be
I’ve had lots of friends tell me that as well.
Just not sure what it would be.

I made sure all hoses and plugs were tight.
Unless somehow the EGR pipe is leaking somehow.
Or like someone else said, maybe the EGR valve took a **** at an inconvenient time
The rattle noise is dependent on RPM
It’ll rattle faster or slower

I’m about to head out and hook my scan tool up and see if I can make a graph like one of the previous comments implied

 

[OrgasmicLarry69]

I hook up the scan tool
There wasn’t a lot I could get regarding EGR and the Crankshaft position sensor
(unless I was reading the wrong values for the different options for EGR graphs)

However I could get a recent freeze frame from the crankshaft position sensor.

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[tpass]

I'm going to say pull the distributor cap and look for rotor contact.. it doesn't sound like metal to me but its hard to tell from a video.... maybe the rotor is installed incorrectly or possibly not the right one?

 

[tinfoil_hat]

Sounds fine for a Duramax.

 

[delta_p]

When I put my MPFI kit in a several years ago on my '96 vortec, I broke a little chip off that vacuum port on the upper intake that connects to the brake booster when i removed it from the manifold. I should have just took the hose off but I didn't. I couldn't find the little piece in the intake when i hunted for it, but I knew it was in there somewhere. I knew what size the chip was because I had the other half and I had an idea which cylinders. I also took a little piece of the vacuum port and burned it to see if it would consume itself quickly. Based on all that and the size of the chip, I figured it would blow itself out the exhaust valve or simply vaporize and I could remove plugs later and bore scope for it was a problem. When I fired it up, sure enough it rattled like yours but not as loud, went away after about 20 seconds. I figured it either ejected out the valve or burned but the truck runs great. I got lucky.

 

[OrgasmicLarry69]

When I put my MPFI kit in a several years ago on my '96 vortec, I broke a little chip off that vacuum port on the upper intake that connects to the brake booster when i removed it from the manifold. I should have just took the hose off but I didn't. I couldn't find the little piece in the intake when i hunted for it, but I knew it was in there somewhere. I knew what size the chip was because I had the other half and I had an idea which cylinders. I also took a little piece of the vacuum port and burned it to see if it would consume itself quickly. Based on all that and the size of the chip, I figured it would blow itself out the exhaust valve or simply vaporize and I could remove plugs later and bore scope for it was a problem. When I fired it up, sure enough it rattled like yours but not as loud, went away after about 20 seconds. I figured it either ejected out the valve or burned but the truck runs great. I got lucky.

Thanks for the help, I don’t know off the top of my head if there’s a hose like that on my intake though, id have to double check.
I have hydroboost for my brakes.
No vacuum assist