Weird rattle when 8>4 cyl. switch...maybe tranny?
Sorry, steveman...been away for a while.
To both of you, I've not investigated this problem any further since I continue to run the non-DoD tune which yields about the same fuel economy with my driving habits...but the problem is still there. On our recent camping trip, I reinstalled the factory tune to give me better highway mileage, and when slowing to a stop the chatter was there.
To both of you, I've not investigated this problem any further since I continue to run the non-DoD tune which yields about the same fuel economy with my driving habits...but the problem is still there. On our recent camping trip, I reinstalled the factory tune to give me better highway mileage, and when slowing to a stop the chatter was there.
I know...been slackin'. Being broke makes it no fun to swing through here/NAIOA and see the awesomeness that has become of some of these rides.
F(most of)ML 
TECH Enthusiast
Joined: Apr 2007
Posts: 697
Likes: 0
From: Hudson River Valley, NY
Well I mean once the engine is warm. I got to run it for like 10 minutes on the expressway and it's gone. On start up....It is not often that I'll get any clatter. If i do it goes away immediately.My engine has been very good except for a small oil stain that I have on the back side of the oil pan. The bellhousing it dry so I think its either coming out a main cap side bolt, crank sensor, or the oil pan gasket. Its not enough to have me tear it up.
Hey guys,
I've got the noise in mine too. Its been there for about 15k miles now. Really loud with the windows open and there is a car next to me on the RH side. GM knows about it. I'm suprised this is a 4 page thread without anybody finding this document:
They say its normal, I don't agree.
I've got the noise in mine too. Its been there for about 15k miles now. Really loud with the windows open and there is a car next to me on the RH side. GM knows about it. I'm suprised this is a 4 page thread without anybody finding this document:
#PIP4440: Engine Rattle Or Tick Noise Worse With AFM (Active Fuel Management) Enabled - Normal Characteristic - keywords BQMI - (Jul 24, 2008)
Subject: Engine Rattle or Tick Noise Worse with AFM (Active Fuel Management) Enabled
Models: 2005-2006 Buick Rainier
2005-2006 Chevrolet Trailblazer
2005-2006 Chevrolet Impala, Monte Carlo
2005-2006 GMC Envoy
2005-2006 Isuzu Ascender
2005-2006 Pontiac Grand Prix
2005-2006 Saab 97x
with 5.3L Engine (RPO LH6 or LS4 Only)
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Some customers may notice a light engine tick or rattle noise while driving the vehicle. This noise will be more apparent with AFM enabled (4 Cylinder Mode) and it may be mistaken for a noise in the transmission. This noise may be the result of normal timing chain slack.
Recommendation/Instructions:
Use a Tech 2 to enable and disable AFM while listening to the front cover area of the engine at a hot idle. If a light tick/rattle noise is heard that increases when AFM is enabled, normal timing chain slack is the root cause of this noise. Only temporary noise relief will be achieved by replacing the timing chain, crank gear, cam gear, and timing chain dampener. As a result, no repairs are suggested at this time. This is currently considered a noise characteristic of this engine.
Subject: Engine Rattle or Tick Noise Worse with AFM (Active Fuel Management) Enabled
Models: 2005-2006 Buick Rainier
2005-2006 Chevrolet Trailblazer
2005-2006 Chevrolet Impala, Monte Carlo
2005-2006 GMC Envoy
2005-2006 Isuzu Ascender
2005-2006 Pontiac Grand Prix
2005-2006 Saab 97x
with 5.3L Engine (RPO LH6 or LS4 Only)
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Some customers may notice a light engine tick or rattle noise while driving the vehicle. This noise will be more apparent with AFM enabled (4 Cylinder Mode) and it may be mistaken for a noise in the transmission. This noise may be the result of normal timing chain slack.
Recommendation/Instructions:
Use a Tech 2 to enable and disable AFM while listening to the front cover area of the engine at a hot idle. If a light tick/rattle noise is heard that increases when AFM is enabled, normal timing chain slack is the root cause of this noise. Only temporary noise relief will be achieved by replacing the timing chain, crank gear, cam gear, and timing chain dampener. As a result, no repairs are suggested at this time. This is currently considered a noise characteristic of this engine.
They say its normal, I don't agree.
Hey guys,
I've got the noise in mine too. Its been there for about 15k miles now. Really loud with the windows open and there is a car next to me on the RH side. GM knows about it. I'm suprised this is a 4 page thread without anybody finding this document:
They say its normal, I don't agree.
I've got the noise in mine too. Its been there for about 15k miles now. Really loud with the windows open and there is a car next to me on the RH side. GM knows about it. I'm suprised this is a 4 page thread without anybody finding this document:
They say its normal, I don't agree.
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No warranty, so no...the dealer is not the answer. There's no evidence of it leaking out, and nothing burning around the engine. I just make sure to check it often and top off when necessary.
Teching In
Joined: Nov 2011
Posts: 4
Likes: 0
From: Michigan
Thank you! I cant believe i stumbled upon this article, because i was going to end up in the cuckoo's nest. Ive had this same mystery "rattle/grind/vibration/whatever" for almost a year now. Had it to the dealership so many times i cant count trying different things to fix it. But as usual, it wouldnt be as noticeable that day or they "couldnt replicate noise"... Ive torn that car apart and was this close to taking my door and dashboard off this weekend. After reading what you guys said i switched my display readout to show the 8 or 4 cyl mode on my way home from work. And TA-DAH, its exactly perfectly timed as you guys said, immediately hitting 4 cyl it starts makiing noise and immediately hitting 8 it disappears. At least i finally have something to tell the Chevy dealer. Good timing too, cuz my certified used warranty ends in August, so i almost gave up. The only difference is i dont hear it with the windows open, mine is only noticeable inside the cabin on the passenger side. It does seem to be getting worse so im glad i found this thread. Soooo, who with this problem has found an effective fix from the dealer yet?
Thanks a ton guys!
Thanks a ton guys!
Teching In
Joined: Nov 2011
Posts: 4
Likes: 0
From: Michigan
Drive just over 25 on a side street with the windows down and ease off the gas until you see it go into 4cyl mode. You will hear it until you go back into 8cyl mode. You can ease on the gas or drop into 3rd which will cause the change back into 8cyl mode and the noise will go away..
Teching In
Joined: Nov 2011
Posts: 4
Likes: 0
From: Michigan
Did they say why GM designed it to start making the noise after 22k miles?? Perfectly quiet before that, then after 22k miles it started getting louder and stayed there. I wonder if they have a random number generator in their design software to make this start happening and mine was set at that mileage...
