Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 20 of 20 Posts

·
Registered
2006 chevy trailblazer_lt
Joined
·
13 Posts
Discussion Starter #1
I've got an unidentified noise coming from the driveline somewhere.

At first I thought it was a loose brake pad, or a brake sheild rubbing just a little bit, because it sounds like a metallic clicking/ticking/rubbing sound, from underneath of the vehicle. It seems to be from the front of the vehicle, but I'm not 100% positive.

It's best heard around 20 mph, to keep the wind noise down with the windows open. It also helps if I'm on a narrow city street where the sound can echo off of the houses.

I've determined that it only happens when the transmission is in DRIVE, and while coasting. Slip it into N or 3-2-1, and it goes away, slip it back into DRIVE, and its back, but only while coasting. It goes away when I get on the gas. It also does it in 2WD, AUTO 4WD, or 4HI, but again, only in DRIVE, and while coasting.

The noise is road-speed dependent. It doesn't go away when braking either.

I put new u-joints in the rear, still have the noise.

At this point, I'm almost thinking it is something in the transmission or transfer case, but only in the final shaft section (yoke, transfer case through shaft, transmission tailshaft, etc.), since it is road speed dependent, and could be driven by the rear driveshaft back through the system. Maybe a clutch pack or band rubbing or rattling in the transmission?

I don't have any definitive ideas of what it is. It's been doing it as long as I can remember.

I'll be changing/flushing tranny oil and filter in the next couple weeks, for the first time since I've owned it. I've got about 70K (highway) miles on it.

2006 TB LT (std wheelbase), 5.3L, 4WD
105k mi

Help please! Thanks.
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Transfer case fluid change is due every 50K, and I'd check the front diff oil level as well. Might be CV shafts - check for torn boots and flung CV grease. No substitute for getting it up on a lift for a listen while it's running.
 

·
Registered
2006 chevy trailblazer_lt
Joined
·
13 Posts
Discussion Starter #3
I looked over the boots when I changed oil and the u-joints 2 days ago, no issues there.

I think it's safe to say that it's not the CV's, given the symptoms and conditions that I list in my original post. Seems to be very dependent on trans gear selection and coasting.

In addition to changing trans oil and filter, I was going to be doing both diffs, and the t-case as well this spring.

And, I will be getting it up on a hoist soon to run it to try and listen closer from underneath.

Thanks for the input!
 

·
Registered
2006 gmc envoy_denali
Joined
·
29 Posts
dont worry i have the same damn thing, get the ticking noise at aorund 29039 in drive ( coasting) with the rpms around 1k-1.1k but if i give it a little little little gas, i can get a different noise then the ticking, but like a grinding noise. if u go to the transmission mods on this fourm ppls are saying its the dod, but heck i want it gone, so if u get urs fixed ( money is tight here) let me know please.


also gm said once that it was my flex pipe and wanted to sale me a flex pipe+ piping+ 2 catalca convertors, got a flex pipe some where else and installed and it didnt fix the problem :9
 

·
Registered
2006 chevy trailblazer_lt
Joined
·
13 Posts
Discussion Starter #5
Can anyone answer these questions:

Does DOD (Displacement on Demand) only function in Drive?

Is there any way to disable DOD?

After reading solaris304's comments, this would help me troubleshoot it further.

Thanks,
Sean
 

·
Registered
2006 gmc envoy_denali
Joined
·
10 Posts
I have had the same noise for 4 years now (06 Denali). Originally my mechanic thought that it was coming from the transer case. He checked it all out and found nothing. The Dealer said that it was not coming from the engine, and the Transmission mechanic found nothing wrong there either. I can only hear it when the engine goes into 4 cylinder mode, and it only happens in Drive. I have been driving in 3rd gear while in the city and I only use the Drive gear on the highway. It is actually quite annoying.... even my neighbours 12 year old Ford truck sounds better? I am due for another vehicle soon and may not be purchasing another GM product.
Until then it would be nice to know WTF it is?
 

·
Registered
2006 gmc envoy_denali
Joined
·
6 Posts
Same Issue with the Rattling while coasting...

So only while coasting at around 35 and below, before the tranny downshifts, and only when the engine is cold. Super loud! goes away if i gas a little or brake. I drove to the dealership to show them and sound was gone! I also just had the engine replaced under extended warranty for faulty push rod bearings, bad lifters and cam. i figured maybe that took noise away but no, its actually a little louder. only difference is it only happens when engine is cold. once it warms up it goes away. :mad:

I'll be bringing it in on Monday night, so they can drive it cold on Tuesday morn and hear it. They mentioned on the phone it might me an exhaust issue. if so, why does downshifting make the noise go away?
 

·
Registered
2006 gmc envoy_denali
Joined
·
6 Posts
Might help us...

One thing we all should do is call the GM owner center and document the issue, apparently i was the first and only case of this this same issue with the noise while coasting. the rep i spoke to today (Lacey) gave me her direct contact info and she did thoroughly documented the issue.

Her number is 1-866-790-5700 ext: 40796

I think if plenty of us call with the same issue and it is documented, we might get the ball rolling on a solution with them. I also mentioned this forum to her and how it's not just me but many of us experiencing this problem. Hope it helps us.
 

·
Registered
2006 chevy trailblazer_ls
Joined
·
61 Posts
I'm sure you've all already found other threads that answer this, but it is the dod or active fuel mgmt.

It kicks in when coasting down to about 17 mph then shuts off. As I understand it, you have to get into the ecm to change it.
 

·
Registered
2006 gmc envoy_denali_xl
Joined
·
32 Posts
I sent my computer to PCM of NC for reprogramming. I did have the DOD deactivated also. Since the tune the noise is gone.
 

·
Registered
2006 chevy trailblazer_lt
Joined
·
13 Posts
Discussion Starter #13
Could probably mark this thread as solved....?

Over the years of scouring the forums (and dealing with the ticking!) since I originally posted (had received PM's with information from various users), here is what I have come up with:

The noise is only present when AFM Active Fuel Management aka DOD Displacement on Demand is active and the engine is running in 4 cylinder mode. This mode can only work with the transmission in D Drive. The only way to deactivate DOD is shift out of drive, or reprogram ECM. From what I've learned, I believe the root cause is the slack in the timing chain changes slightly when the engine goes into DOD 4 cylinder mode. The tick we are actually hearing is timing chain slap.
 

·
Registered
2006 gmc envoy_denali_xl
Joined
·
16 Posts
Any other solution than reprogramming

Is there any other solution to this problem other than reprogramming the PCM? Like fixing the timing chain slap? The noise wasn't there when I bought the car. There has to be a different fix.
 

·
Registered
2006 gmc envoy_denali_xl
Joined
·
32 Posts
I don't know if there is. My noise is gone with the reprogram so I am happy. If you want to tear it apart and look at it go for it. Let us know what you find.
 

·
Registered
2005 chevy trailblazer_lt
Joined
·
11 Posts
I had the same noise on mine it ended up been the fan clutch change it sound is gone
 
1 - 20 of 20 Posts
Top