Finally a video of my rattling car

[Spykem4e]

Hi guys,

Last year I posted a thread about my 2005 CTS rattling under low-mid acceleration.

The car is a 2005 3.6l auto transmission. 277 000 kms on the odo and the rattle started at around 177 000 kms.

To make the noise, the car has to been accelerating (not on park), the engine has to be in normal temp. The rattle only exists when there's light to medium throttle at 1750 rpms to 2400 rpms max and disappear if higher or lower than this. During the winter where the temp drops below 0 C, the noise goes away.

I've changed fuel filter, transmission filter, transmission fluid (every 50k) and always looks pretty good red when changing it.
Engine oil always changed, good results with UOA, always used synthetic, never drop below min on the dipstick.
I've changed timing chains and tensioners to make sure but the sound is still there. You can hear it at around 5-6 sec. I tried additive in the fuel, higher octane fuel and nothing works.

Here's the video:

http://www.youtube.com/watch?v=2DC0S1RKq2A

If you guys have any idea, please let me know!

Another video if its helping:

http://www.youtube.com/watch?v=uoYVm1j1QYY

 

[Nick R]

Sounds kinda like the Serpentine tensioner that was on my cavalier when I accelerated. The belt tensioner would rattle and vibrate on acceleration, at about those RPMs.

 

[Jim Spahr]

I listened to both videos and couldn't hear the rattle. Can you get the mike closer to the engine? Do you have any CEL/MIL displayed? Have you checked the TSB's for others who have had similar rattles? My first guess without any additional info is the EGR is causing 'pinging' or engine knock and that's what you are hearing. That condition is in the range of your description.

 

[Spykem4e]

I checked belt tensioners, pulleys, alternator and everything is perfect. I listened to them with a stethoscope and could hear an abnormal noise.

Inside the engine, it is very quiet.

I don't have any CEL/MIL displayed and no code in the computer history or current. I've checked TSB and there's 2 things I could find:

-a tsb about 3.6l SRX (same engine as mine) in 2004 about air inlet tuning control valve actuator that could make a buzzing/rattling noise while accelerating but also could be heard on idle.

-a tsb about de-carbonizing the combusting chamber.

If I had a bad knock sensor, would it trigger the CEL?

For the info, the first video, at 5 seconds from the beginning, you could hear the rattle for approx 1 to 2 seconds. Sorry but the microphone on the Iphone is not that accurate. You have to concentrate to hear it. But in the car, you can hear it like it was metal to metal grinding/ratcheting noise. Its not a buzz sound like an heat shield.

Could an exhaust leak could cause a similar sound?

Its heat related for sure!

 

[Warstud]

I couldn't here anything....could it just be spark knock? Try a higher octane gasoline.

 

[Spykem4e]

here guys, I made another video during uphill yesterday.

the rattle starts at 0:13 on the video.

http://www.youtube.com/watch?v=wCbi3FnuhTM

Help me find the rattle because I'm going nuts!

It only happens during light to medium load, summer time only a/c on or off. The car requires 87 octane fuel but on the video, its with 91/94 octane (for the past week and a half).

 

[The_Eric]

Sounds like some detonation to me, but it's hard to say for sure. Does the 3.6 have an EGR valve? If so, see if you or the dealer can verify it's operation...