2000 Impala 3800 - Rattle / Loud Click on startup

Help!
Our 2000 Impala w/3800 V6 is making a ticking/rattling type of sound upon startup in the AM. It goes away (or gets so quiet you can't hear it) when you put it in gear. After a few miles of driving, the sound
goes away entirely.
I first heard this noise during the warranty period and the dealer could not reproduce the problem. Then the transmission failed at 46K, and we had it rebuilt. After the rebuild, I noted the noise again and called the tranny shop. They suggested it was probably an engine problem, so we took it to our maintenance shop and they could not reproduce the noise until my wife came to pick up the car and started it up. They listen and are quite sure it is a tranny issue. So, we take it to the tranny shop (which also has an full-service engine repair shop next door) and they can't reproduce the problem until my wife goes to pick up the car. They get an engine guy and a tranny guy out there to listen and they believe it is an engine problem. We bring it back to them a couple of days later so they can cold-start it, and after some diagnosis, the engine guys send it back to the tranny guys. The tranny guys then proceed to pull the transmission, replace the pump and the TC, reinstall tranny and THE NOISE IS STILL THERE.
They state they are stumped and don't know what could be causing the noise. I call the dealer and ask about "piston slap" as a possible cause. "not on the 3800" he says.
Has anyone seen this issue before? What could be causing this rattling noise that goes away when you put it gear and drive a little.
Sorry for the long-winded post. Thanks in advance for any ideas. We are at wits end.
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Does it go away if you just let it run?, not drive it. When and how did it start? In this environment for us to diagnose a noise that several mechanics are unable to, is just about impossible. Check with the dealer see if there are any tsb's relating to this condition.

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It have not let the engine run it for a long time without driving, so I can't answer the questions. I have let it run for several minutes (10-12) while trying to determine where the noise is coming from, but it does not go away. The noise seems to be coming from the top of the engine on the drivers side. Driving the vehicle for a few miles makes the sound go away. No codes, no drivability issues. Just a lot of concern about the interaction between the noise and putting the car into gear (which makes it go away). Given that the tranny failed at 46k, I would like to understand why putting the car in gear makes the sound go away.
I do realize that it is going to be next to impossible for anyone to diagnose, but I was hoping that someone may have had similar experience.
I will be taking it to the dealer tomorrow night for a cold-start test on Friday AM. Looking to gather any information I can to give to the dealer.
I have read a couple of posts on ImpalaHQ.com that pertain to engine rattle on cold-start, and in those cases the dealer says this is normal for the vehicle (stock answer when they can't figure out the problem).
Thanks for the reply Shep.
Shep wrote:

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Forgot to mention, when it started. We bought the vehicle new, and I noticed the issue at about 22K, nearly three years after purchase. Took to the dealer at that time and could not reproduce. It is the wifes car, and she plays the radio so loud, she never hears any noise until it is too late. How did it start? As far as I know, there are no specific events related to this problem starting. It has been intermittent until recently.
Thanks again.
SHOMan wrote:

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SHOMan wrote:

So you can get it to make the noise with the hood up? If it makes the noise, shut the engine off and restart it and see if it still makes the noise. Then you can start to isolate external parts.
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Eugene Nine wrote:

It makes the noise whether the hood is up or not. The noise is emanating from the area where the tranny is bolted onto the engine. I found no evidence of loose parts that could be causing the rattle, and further, the speed of the "tapping" goes up and down when you rev the motor, suggesting an internal part. It sounds a lot like someone is hitting the block with a piece of metal.
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I believe there is a tsb for a chain drive support bearing in the trans that has your general symptoms, check your dealer or trans shop.

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you can sure worry yourself to death about that chain noise but it would be much easier to accept it as normal......cause it is. i didnt say it was pleasant, just that it was normal.........kjun
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KJun,
If it is normal, then why is the loaner Impala (same motor) we got from the dealer quiet as can be?
The dealer has diagnosed it as a tranny issue, and it will be going back to the tranny shop where the owner states he will install "new" rebuilt tranny.
Thanks to all who have replied. Very much appreciated.
KjunRaven wrote:

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SHOMan,
The problem is most likely not in the engine (3800s are NOT known for piston slap) but in the transaxle. On the 4T60Es in the 90s (very similar transaxle to the 4T65E in your Impala) GM had an issue with a rattle or growl on startup caused by cavitation in the transaxle oil pump, the secondary effect is for the oil pressure to "bounce around" and cause the regulator valve to rattle. GM even admits in an information bulletin (Buick # 80-71-04 dated April 8, 1998) that the problem is because of the design of the pump but that they have no plans to change it (at that point the 4T60E was near the end of its production run, to be replaced by the 4T65E). You could replace the pump and it will NOT cure the problem.
GM further states in that bulletin that the problem, while not normal" is benign - it will not cause transaxle failure, and that the noise can continue for as long as 4 minutes after startup (until the trans fluid heats up a bit).
Since I've not worked on the internals of any 4T65Es I don't know if they are afflicted with this same problem or not.
My '94 Regal has had the "problem" since about 15K miles (now at 108K) and has not gotten worse (and the noise is not that loud to begin with). Goes away after about 15 seconds on my car and does not return until the transaxle has sat long enough to return to ambient temp.
If they swap out your transaxle the noise may well disappear - and then again it may not. It is going to be a crapshoot.
That's about all I can add - maybe Ian or one of the other dealer techs that are in the newsgroup have some additional info..
Regards,
Bill Bowen Sacramento, CA
BTW, there is a factory-approved diagnostic procedure to isolate the engine from the transaxle for noise diagnosis. You remove the flyweel cover, mark the mating of the torque converter and the flywheel, then unbolt the torque converter to flywheel bolts, then push the torque converter all the way back towards the driver's side. Start the car - if the noise is still there, it is engine: if not, its transaxle. Note that on some cars this procedure will cause the "Check Engine" light to light and a DTC to be set, whcih you'd need to clear.

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Bill,
Thanks for the great explanation of your experience. It does seem plausible that the same thing is happening in the Impala.
Can you help me understand why some vehicles would have this problem and some would not? Or is it a matter of not IF, but WHEN.
So far, yours is the most logical sounding theory I have gotten from anyone.
Very much appreciated! Thanks again.
William H. Bowen wrote:

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SHOman,
Don't have an explanation - at least not an official one. GM has never (to my knowledge anyway) actually come up with one.
My personal theory (and let me say again, this is only my own theory) is it is a stackup of tolerances. Depending on how all the clearances in various items in the main case, channel plate etc. stack up determines whether the pump has problems drawing up fluid when it is cold and also the amount of cavitation that results.
This is why I suspect that if they change out the entire transaxle the problem may go away (totally different set of parts with their own "stack up" of tolerances).
It is like the situation of 2 identical cars that get different gas milage even if driven by the same person.
Now if anyone else wants to add to this, I'm totally open for comments (even if you think I'm full of hot air).
Regards, Bill Bowen Sacramento, CA

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KjunRaven wrote:

> Sorry for the long-winded post. Thanks in advance for any ideas. We

I'm curious why you feel this is a "chain" noise. What chain are you referring to?
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Mike,
All GM (and a lot of other) tranaxles use a Morse chain to transmit power from the output of the torque converter to the gearset section of the transaxle. GM was actually ahead of its time when they first used this technique on the 1966 Toronado.
In this case I don't believe the problem is chain noise - I'm more disposed to noise created by combo of oil pump starvation and pressure valve (know problem with 4T60s).
Regards, Bill Bowen Sacramento, CA
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Well there you go - ya learn something new every day. Thanks Bill.
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This reminds me of my buddy's Ford F150 truck, it would rattle upon start up, and the noise would bounce around so bad it was hard to pinpoint it, and the ticking speed correlated to the rpms. Thus, when we'd switch between Park and Drive the rpms would change and so would the ticking speed and volume, which is why we thought it was internal and tranny related. When driving it was less noticeable but still audible enough to annoy. After a few miles of driving his truck and reaching normal temp his rpms would drop to normal at idle and the ticks would *almost* disappear. Anyways, it ended up being external, it was one of the brackets used to lift the engine out of the truck. It was connected to the exhaust manifold and one of the two studs that held the bracket was broken and causing it to rattle like crazy. The way we found it was I grabbed a hold of the bracket and it muffled the ticks. Not that I recommend grabbing random parts with the engine running. Maybe using a prod extension to feel around the engine to feel where the vibration is strongest might help. Just a random thought.
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