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.
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.
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
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
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.
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.
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.
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"
Thanks to all who have replied. Very much appreciated.
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
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..
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.
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
Very much appreciated! Thanks again.
William H. Bowen wrote:
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).
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).
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.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.