That "rattlesnake" sound

[JimWilson]

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.

[battmain]

Same issue here, but still can't find it. I'm thinking valve train now. If I could find my stethescope I probably have a better idea where its coming from, but I can't really tell while under the truck or listening from the top with the engine running. Before it happened, I was getting a clanking after using 4wd low to move the trailer up a pretty steep driveway. After the clanking went away, the sound appeared. I was reading something about the transfer cases and think it might be coming from there. Since the truck is way out of warranty. It's gonna be fixed by me.

[mdrag]

JimWilson,

You started this topic on 02/23/04 (http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=15;t=000197) and posted two links. I believe the second link describes the infamous cold start piston slap.

Could this be the 'rattlesnake' noise that your are describing?

[JimWilson]

No. I have CSK too, and that makes a very distinctive sound (kinda like an old diesel :D ). Those two sounds are definitely different.

[Lawnboy]

Just a Wild guess....Could you be hearing your EGR valve chattering?

Supposedly they have a newer type that doesn't have the moving valve inside.

[Heavy Duty Neil]

Jim, a co-worker has a '03 1500HD that I think makes the same sound. I have only driven it once, so it's hard to say for sure, but I think the noise is coming from the cab vents that are behind the back seat. My truck doesn't make that noise, that's why I noticed it on hers. Maybe you can mess with the vents some (tape them shut?) to rule it out of the possible noise makers.

Another possibility is maybe the muffler. Mine sounds like crap when I first get in it in the morning and drive it a quarter-mile or so. I don't know if it's a loose heat shield or if there is a baffle loose inside the muffler...whatever it is, it usually goes away once it has warmed up.

[JimWilson]

Mines definitely coming from the engine, somewhere along the top more then likely. It's not in the cab, or the exhaust.

[JimWilson]

Originally posted by Lawnboy:
Just a Wild guess....Could you be hearing your EGR valve chattering?I guess that's something to consider. Where is the EGR? I assume it's on one of the exhaust manifolds.

[nutfarmer]

I have the same rattling sound. Happens only when cold (i.e. first start-up), but the outside temp can range from a cool morning to a hot afternoon. I think its the turbo not having any oil to the bearings yet. It seem to go away after about 30-60 seconds of run time.

[Lawnboy]

The EGR valve is located on the rear of the drivers side valve cover. A little plastic line with the valve at the end. It slips into a grommet on the valve cover. Just pull it out and shake it.

Now that I think about it, you'd have to have superhuman hearing to be able to hear the EGR valve in the cab. Usually it requires popping the hood to hear it, and engine/fan noise usually drowns it out some.

Did you have it in to your dealer about this?

Other things it could be....

Exhaust leak?

Valvetrain noise?

Is it engine speed or half that?

[JimWilson]

Originally posted by Lawnboy:
Did you have it in to your dealer about this?Yup, and I got the standard answer I hear from them on virtually everything; they all do that. But for some reason he wouldn't allow me to test any of the "other" vehicles that supposedly have this exact same sound.


Originally posted by Lawnboy:
Is it engine speed or half that?It's most noticeable between 1000-1500 RPM, with the noise being the loudest around 1500. It rises and falls in step with the RPM's, so by 1000 it's almost imperceivable.

[Heavy Duty Neil]

Originally posted by Lawnboy:
The EGR valve is located on the rear of the drivers side valve cover. A little plastic line with the valve at the end. It slips into a grommet on the valve cover. Just pull it out and shake it.You are talking about the PCV valve. The EGR valve is right next to the oil fill cap on the passenger-side of the 6.0 gas engine, it's about the size of a coke can. If it was bad, you'd probably get an SES light.

Check the heatshields around the sparkplugs & exhaust manifolds. Bend them around a little to change how the vibrate.

ps. Maybe a baby rattlesnake crawled into the airbox and is waiting for you to change the airfilter. tongue.gif

[JimWilson]

Originally posted by Heavy Duty Neil:
ps. Maybe a baby rattlesnake crawled into the airbox and is waiting for you to change the airfilter. tongue.gif At this point I'd rather that be the problem. At least I'd know how to fix it then. :D

[Lawnboy]

Geeze....Sorry guys...my bad!

I meant PCV valve, NOT EGR Valve! :rolleyes:

I even proof read my posts, and didn't catch it.

[battmain]

Just thought you'd like to know, if you leave the sound long enough, eventually it will make a sound where you say "Uh Oh." The sound was bad enough for me to abort a trip to the race track over the weekend and I got 200 miles closer to home before something went completely. (No drive.) So it's either the torque converter or the transfer case. I'm thinking torque converter because as I was coasting to a stop at the side of the road, I switched to 4wd high and felt a jerk like it engaged and another jerk when it went back to 2wd. 64k miles on the truck. I'll find out when I get around to it or decide if I'm going to let the dealer handle it. It's been an expensive weekend already and I didn't even make it to the track. :(