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Rattle in Engine

I started out by taking my car in because of a rattle under the engine and here I am $5,324.00 later and still the rattle is under the engine. You can’t hear it if you are standing outside…only from the inside with the windows closed and only if the car has sat overnight for at least 10 - 12 hours and only up until the car warms up and then it is gone. After the initial warm-up, If you stop the car and it sits for 2, 4, 6 hours and you turn it on - still no rattle…it has definitely confounded my mechanic who has seen it 5 separate times totalling about 1 month without my car…they have put new timing chains and everything that entails and new tires and the list goes on and on and, yet, here I am with the same rattle I originally took in for 1 1/2 months ago…I told my mechanic this morning, “I am done with taking it in and having you guys guess and try to pinpoint what might be wrong with the car…if something else comes up, or the initial rattling gets worse, and if the check engine light comes on, then I will take it back!” What could that rattle noise be??? HELP!

Cadillac CTS . . .

Model-Year ?
Approximate number of miles ?


$5,324 worth of work and he still has no idea what’s causing the rattle? Man, you are correct in going elsewhere.

What year is this Caddy CTS and how many miles does it have on it?
Does the rattle do so in synch with the speed ofo the engine or the speed of the car?
Can you list for us exactly what your guy has changed so far, and if possible what he’s done diagnostically?
Do you know if he has used any equipment, such as a mechanic’s stethescope or a little device attached to the engine that feeds a signal to a screen (called a “linear accelerometer”, it meausres vibrations and displays them on a screen).
Have you left it with him overnight?

I’m going to wildly guess that you have hydraulic tappets (lifters) that are collapsing overnight. They’re hydraulic devices that fill with oil and expand to keep the “play” between the valvestems and the elements that push them filled. Sometimes they their insides become sticky and allow the oil to drain out overnight, letting the valvetrain clatter.

But that’s a wild guess. Having answers to the above questions would help greatly.

i’m thinking the 3.6l v6 timing chain and the guides

ok forget that

I’m in agreement with mountainbike that this problem might be related to a failing valve lifter; more multiple failing lifters.
You could try an additive such as SeaFoam or Berryman B-12 in the engine oil and see if this helps.

Five plus grand worth of wandering in the desert? Ouch.

If you are willing to get dirty, jack the car up on stands and after sufficient cool down start the car and get under it. The noise may be caused by a cracked exhaust manifold or a catalytic converter.

I had a problem on my Corolla with an alternator that would rattle, but only if it was under load charging the battery or powering the headlights. Might be a possibility, as the battery will discharge somewhat overnight, which means your alternator would be under a heavier load if the car has sat overnight. Does the rattling stop after the car has been driven for a half hour or so? Does this occur more in cold weather? Does it sound louder if you turn on the headlights to full bright? All would be confirming of the alternator theory. A mechanic could use a car stethoscope to determine more exactly where the sound is coming from too.

Me? I just live with it.

Here are the answers to questions asked above: Cadillac CTS - 2005 - 107,000 miles. Here is what my “used to be” mechanic has done to the car so far: Replace Both sides Front lower control arms, replace struts, replace both front tires, replace alternator drive belt tensioner, replace both valve cover gaskets,replace all 3 timining chains and everything that entails - this has cost me $5,342! It rattles most as you accelerate when completely cold and after having sat for over 8 hours. I do not know if my mechanic used a mechanic’s stethescope. Furthermore, he told me it now needs front brakes done (I can believe that as it has been awhile since I last did them andhe quoted me $270) and the back vehicle differntial carrier bushing mount - this for another approximate $500!!! If it is the hydraulic tappets that are collapsing overnight, what do I do to fix that…I saw that someone else suggested I use SeaFoam…pls help and let me know if you think that $500 is a good quote for the carrier bushing mount. Thanks so much…very frustrated and have had to borrow much to pay completely pay the first $5342!

Try the seafoam. It’s available in a bottle at any parts store. Follow the directions to the letter.

And get a different shop. An independantly owned and operated shop with a good reputation. Tell him what your current guy said, but be clear that you want a second opinion. Also ask him about the rattle.