That "rattlesnake" sound

JimWilson · March 5, 2004

My truck is an 02 Silverado 2500HD with the 6 liter motor. I've got this weird sound coming from my engine. It only seems to happen when it's cold, and when I'm going slow. Here's the story.

I live in one of those typical residential areas. In order to get to any main roads you have to go a block, stop, go another block, stop, go another block, stop, go... well, you get the idea. When my truck is cold it seems that as I'm coming up to a stop sign when I lift my foot off the gas I hear a sound that is the EXACT same sound as a rattlesnake would make (AAMOF, that description comes from one of my daughters: "Daddy, it sounds like there's a snake in your truck!"). It happens every single time; as soon as I take my foot off the gas you hear it, but just for a second or two. It starts out quite noticeable and then fades quickly, usually before I come to a complete stop. When I get to the next corner I take my foot off the gas an it happens again. Like clockwork.

It seems to go away when the engine has warmed up. Naturally, the dealer says they can't duplicate it, which is BS because I told them exactly how to reproduce it.

Anyone have an idea as to what this noise can be? It's getting kind of annoying.

PewterC3 · March 5, 2004

mine too.

March 5, 2004

Here's my reply from ChevyTalk for those here who may not visit that forum:

Mine does the exact same thing. After the engine has been running for about 2 minutes, it starts doing it between 1400 - 1600 RPM. Bad enough to make me call my truck a Clackerado. Anyhow, after the GM rep listened to it along with my warm start low-end knock, they're putting in a new engine in it on Monday. The sounds both were present at 1,200 miles and the rig now has 6,000. It's a '03 2500HD w/ a 6.0L.

Jeff

PewterC3 · March 5, 2004

I read something somewhere that one of the engines that has been replaced had 2 cylinders overbored.

superbee · March 6, 2004

That is a sin. GM should be kissing every buyer's butt who has one of these lemons. This just disgusts me, the price we pay, then to be patted on the head and be told by some HS dropout that "It's common and not a problem". Sorry bout that, kinda got a little heated.

PewterC3 · March 6, 2004

Sure it's annoying...but I'm not sure it is really a PROBLEM. My dad has over 200k miles on his 5.3 and it still burns less then a quart of oil between changes.

cbz2500hd · March 6, 2004

That noise that you have is not normal. Mine just like Jeff B. does it all the time.

The rattlesnake noise is coming from your pistons. I had a service manager tell me that the cause is bad wrist pins others called it piston slap either way it's a flaw in your 6.0. I lemon lawed mine no cost to me manufacterer pays cost.

Chris B.

superbee · March 9, 2004

Not a problem? There are pistons baning around inside the bore and maybe it's a problem? I wouldn't put up with that from a $200.00 lawnmower, let alone a $40,000.00 vehicle!!

March 9, 2004

I agree Superbee! It wasn't there when I bought it, I sure don't want it after the sale!

Chevyfreek · March 9, 2004

GM is not doing a great job dealing with these CSK issues. They have a defect in their manufacturing process somewhere with all the reported cases of CSK. This problem is supposed to be cleared up for the 04's so we will see what happens. If this is the case GM should be putting the new 6.0L in any truck that is suffering from the CSK, because it is just the right thing to do. And we all know they want to do the right thing....

jhill · March 10, 2004

My dad has this issue with his 01 tahoe, and another friend had the same problem with an 03 Z-71. Both were successful in getting a 5 year/100000 mile powertrain warranty out of the whole problem! Evidently its all up to your dealer and how willing they are to help out. I hope my 6.0 doesnt develop the issue

JimWilson · March 10, 2004

I don't think is the CSK issue, because I have that too. When I first start my truck it sounds like a diesel for up to a minute, then it quites down (for the most part anyway). This is a lighter sound, and only happens when I let off the gas coming to a stop. And when it warms up the sound disappears.

als1984z28 · March 13, 2004

I have the same noise in my truck. It always happens when I am pulling up to a stop sign and I let off of the gas. It doesn't happen after it warms up. I am also getting a loud ping in the rear of the truck. I don't know if it's the gas tank expanding or the rear end (G80) is messed up. The rear still seems to work correctly, so I guess its time for for a trip to the Chevy garage. What I don't want to hear is, "Everything checks out fine, we couldn't reproduce the noise that you think you hear." I have had that enought with my P.O.S. Mitsubishi Galant.

GMCTech · March 14, 2004

I have responded to this concern on many other forum boards - Here is the explanation and the recourse you can take.

The noise that you are hearing is produced by the valves. The valve guide clearance is the tightest of any vehicle produced to my knowledge. When the vehicle is cold, the heads, and thus the guides are slightly contracted (it only takes .001" to cause this noise!!!). This causes the valves to "stick" and then get get forced shut by the valve spring, making your click.

As the head heats up the metal expands and you get your valve guide clearance back.

Don't just pass me off as the next jack-a@@ wrench turner who doesn't know what he's talking about. I have personally removed, inspected, rebuilt, machined and installed a number of heads.

The cold to hot change in these motors is about .004" in the valve guide. To measure clearance, you are required to use a micrometer that has a tolerance of .0001 (that's 10,000ths !!)

The Vortec motors have the tightest tolerances out there. You may say that is an engineering flaw, and I don't necessarily disagree that this type of tolerance is necessary.

Now, as to your recourse. Go to your dealership. Have them generate a repair order with your concern on it. Have them diagnose the sound. Get their statement that it is normal. Call 1-800-GMC-TRUCKS, Address your concern with them. Be sure to get copies of everything.

Every customer that we have sent down this road has gotten an extension on thier motor warranty coverage up to 100k miles. If you are not convinced after 100k miles that this is not a problem, then you have a bigger problem than I can help. We have many customers with 150k -200k + miles on their trucks, still with valve clatter and still running just as strong as day 1.

THERE IS NO DAMAGE BEING DONE TO THESE MOTORS AS IT IS NOT A TRUE CONTACT OR LACK OF LUBRICATION ISSUE!!

I hope that this addresses the issue at hand, and has answered some questions and concerns.

superbee · March 14, 2004

If this is not "true" contact, why does the valve "stick"? I am not doubting you, just trying to understand. I am just the next dumb wrench turner. Maybe my memory of Langmuir's theory of lubrication is a little hazy. Please enlighten me.