chattering sound from engine bay

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Hi guys, tonight I was with a friend who just bought a used 2007 cadillac cts with the 2.8l. He was so happy that he called me to show me his ride and trying to compare with my 05 cts.

Short story: When idling, his engine has a weird sound and from the cadillac forum, most people say it could be bad timing chains. There's no check engine light and when I test drove the car, it was running number one.

There's kinda of a fluttering, chattering sound coming from the engine bay. We compared both engine sound and mine doesn't do it. So I called my boss, who has a 2.8l just like my friend and we compared the sound. The sound is only coming from my friends engine.

What I did, and tell me if I'm wrong, I took a screwdriver, I put one side on the front of the engine while the engine running and my ear on the other side of the screwdriver to pinpoint the problem. I've tried different places from the engine and each engine (both 2.8l and my 3.6l) as similar sound coming from inside the engine.

Now my question is this: could it be a serpentine belt since its looking like coming from the front of the engine? There's 2 belts but when you look at the one on the passenger side, you can see the tensioner shaking compared to the other one. When the engine is idling, you can easily hear the sound. When you rev the engine, you can hear it fluttering/chattering more but above 1200rpms, you cannot hear the sound anymore.

Now, I don't want to put the screwdriver on the belt neither on a pulley while the engine is running in case I mess something there but is there a way to check if its the belt or a pulley?

His car has 80k miles as far as I know compared to mine with 122k miles and I never changed the belts yet because the owners manual says to change it at 140k miles. Since I didn't need to change mine, I said to myself that my friends one is suppose to be good for another 60k...

Any input appreciated!
 
Timing chains would not throw a code! I am not an expert though on the engine you are looking at though. Timing chains do not do anything until they fail normally a tensioner when it fails will allow the timing chain to slap around on start up but most times it goes away once the oil is flowing nicely.

How many miles on this engine? Dirty or clean when you look through the oil fill hole?
 
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could it be a serpentine belt since its looking like coming from the front of the engine? There's 2 belts but when you look at the one on the passenger side, you can see the tensioner shaking compared to the other one. When the engine is idling, you can easily hear the sound. When you rev the engine, you can hear it fluttering/chattering more but above 1200rpms, you cannot hear the sound anymore.


Well, you've identified something un-right. I'm sure they made it much too difficult to just remove the belt to see if the noise goes away. By that I mean that it surely won't be a 'turn your head and cough' exercise. It's assured to be a process.
 
John, his car has 80k miles approx. Unfortunately, you can't see through the oil fill hole see its a "L" shape same as mine. I checked the oil on the dipstick and it looks fine just like mine after 2k miles. I don't think its inside the engine since I've tried to listen inside the engine with a screwdriver and couldn't find any weir sound compared to mine and another car.

Gary, I can try to take off the belt to see if the sound disappear but just for my knowledge: Is the car going to start even with the belts off? Is it going to do any harm on the engine or water pump or something else? (its sad to see that I don't know that answer when I can do my own brakes, do a body work on my car, changing plugs etc.)

The way I see it when I look at my engine, I have to take off the air intake assembly right before the throttle body to access the belts. It looks like an easy job at first sight...
 
My self I agree with the belt tensioner. they do make a weird knocking rattle when they fail. Peel the belts off and start it, just don't run it long! It should be apparent quickly if thats the issue. Roll over the pulleys and see if theres any bearing noise too, its good insurace to check them every now and again anyways. Hope that helps.
 
just an update, I took the hose from his house and threw water on each pulley and the sound disappeared and reappeared after couple of minutes. So I think is bearing related. I lubricated them and I think its the tensioner pulley. So next week we will undo everything and try to find out the right pulley to change.
 
Gety a metal bar, long screwdriver, stethescope, or something like that and actually listen to each pulley. It'll be obvious which one is the culprit.
 
Originally Posted By: JohnBrowning
Timing chains would not throw a code!



But if they skip a tooth they will cause a code.
 
Originally Posted By: GMBoy
Originally Posted By: JohnBrowning
Timing chains would not throw a code!



But if they skip a tooth they will cause a code.


Didn't he say the CEL was/is NOT on?
 
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Originally Posted By: gathermewool
Originally Posted By: GMBoy
Originally Posted By: JohnBrowning
Timing chains would not throw a code!



But if they skip a tooth they will cause a code.


Didn't he say the CEL was/is NOT on?


No mention of the light on on the OP. I was just commmenting to John.
 
It's the Serpentine belt. Our 4.0L V6 mustang does the same thing when the AC compressor is on. When it kicks on, the tensioner flutters and it makes a rattle noise. It took me forever to find it. Tomrrow I'll try to make a video of it to showcase it so you can compare.
 
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rudolphna, thanks for the video!

My friend ordered the 2 belts so we have to wait for a week or so. Since then, I'll have the time to see the video :)

Just for your info guys, there's no check engine light.

We started the car yesterday since the car was parked in his driveway for more than 12 hours and you could hear the chattering sound for the first 3 secs, very loud. Looks like a pulley needs to be change!
 
Originally Posted By: GMBoy
Originally Posted By: gathermewool
Originally Posted By: GMBoy
Originally Posted By: JohnBrowning
Timing chains would not throw a code!



But if they skip a tooth they will cause a code.


Didn't he say the CEL was/is NOT on?


No mention of the light on on the OP. I was just commmenting to John.


My comment was meant toward John's statement. I didn't mean to quote you as well. Sorry for the confusion.
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rudolphna, thanks for the video.

Exactly like the video, I can see the tensioner moving, rattling and the sound it makes, its louder than your video but its almost the same!

Thanks a lot, I will try to find a tensioner used! So when I'll change my friend's belts I will change the tensioner at the same time.
 
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