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Engine Noise.. (help identify)

2004 Buick Century. 3100 motor. 150k miles

Recently discovered strange noise but not sure exactly how long its been happening. (I listen to the radio pretty loud)

Engine sounds normal at start/idle (hot and cold)
During acceleration i hear a constant ticking/tapping/clattering at a decent volume from 1st to 3rd…after 3rd it quiets down a bit but still constant. It goes away completely directly after shifting into 4th.
i then cruise down the highway at 75-80 with no problem whatsoever.
(It can also be heard if i rev the engine in park.)

the day i noticed it i immediately checked the oil. It was a little over a quart low. I filled it but the sound has not changed.

any ideas?

I wouldnt say its a full on knock but it does sound alarming like the engine could blow at any moment from 1st to 4th. Sounds perfectly fine after that.

This is anyones guess. No possible way to diagnose something like this from a computer desk. This is one of those that needs ears n eyes onsite.

I was going to say its the valve lash adjustment…but you say it sounds normal when stationary. From your description it sounds tranny or driveshaft related possibly…very hard to say. If I heard it with my own ears…thats a different story. I know how fast driveshafts spin so you can sometimes tell by the cadence of the sound… Ive gotten almost mystical with this learned skill…takes a while to develop but its led me to more solutions than head scratching.

Hope you figure it out.


wow I don’t know why my post is in 1 block of text… I tried to break it up when I typed it…

anyway… thanks… I would say it may be driveshaft related too… since ive been listening to it I sometimes hear a whistle type sound from the rear end as well… and sometimes the tranny bucks from 1st to 2nd.

Since you can hear it when you rev the engine in park I am going with engine noise. Try changing the oil and adding a can of Restore. I had 2 cars with this engine and they can get a bit noisy as they get older. Also keep an eye on the coolant, these engines have weak intake gaskets that can go if they have not yet been replaced.

Actually you seem to be describing a Pre Detonation scenario.

Again…this is impossible trying to diagnose in this manner. Trust me…the right person will know exactly what that noise is…and they would need to be onsite.


You might not hear it at highway speeds because road noise is too loud.

The noise you’re hearing might be from a stretched timing chain.


Thanks for all the suggestions and input!

Honda, my father is also extremely good at identifying sounds (he even diagnosed a noise over the phone one time LOL) but hes out of town and wont be home for a week -.- ima call him and describe it and see what he says.

jtsanders, im pretty confident it stops. Like the road noise doesnt seem to get any louder from 1st to 4th but the noise just stops directly after the shift.

tester, i also considered the timing chain smacking the top of the cover. I had to replace the timing chain on my other 3100 motor too.

ill come back and update when i figure it out.

It’s unlikely to be driveshaft related if you can still hear the noise with the car stopped in neutral. One idea, ask an assistant to hold a short piece of garden hose to their ear as a directional stethoscope and move the other end around in the engine compartment to see if they can better locate the exact location the noise is coming from.

update I am now under the impression that its a lifter or rocker. Got time to check it out a little more today…the racket is coming from the top of the engine…its the loudest in the front corner. Im going to remove the valve cover when i get time and check it out.

Agree with the idea that it might be a failed valve lifter. Or a damaged cam lobe. This is a pushrod engine with roller lifters so the damaged cam lob isn’t likely - but possible.

Some engine oil additives like Marvel Mystery Oil can loosen a stuck lifter, if you are lucky.

update did an oil change and subbed 1qt of oil for 1qt of rislone oil treatment. No immediate improvement so far (idling in driveway) but i will drive the car a bit and give it some time to do work.

If nothing changes i will park the car and begin digging deeper internally.

These engines are likely to be abused in an oil change manner… Which creates accelerated wear and larger than normal clearances. So…hearing one noisy doesnt surprise me much.

Your next experiment after the rislone…is to add a quart of 85/140 gear oil if it quiets down after that…you found the issue… too large o clearances.

Tester made a very good suggestion a while back within here… Cam chain. Certainly possible.

When you have done this for a while…a long while…your ear will tell you which noise this is. We are starved from some of the biggest clues here on this forum…sight and sound. They play a bigger role in this stuff than you could possibly imagine…not a recording…live and onsite. When onsite you can move and see how the sound changes…where it is localized etc…you get the idea.

We could discuss this for weeks on here…when a 15 second onsite listen would nail it…it really is like that.


So ive taken the belt off and ran the car to eliminate all the pulleys on the motor as a possible noise source. The sound remained.

Im confident that its either a bad lifter or rocker arm/push rod

was looking up prices on these components and cant find rocker arm replacements? Are these dealer only? Seems silly.

You have to hit the return key twice to create a new paragraph.

The 3.1 engine is a growth of the older 2.8 engine. On the 2.8 engine, the hydraulic lifters were adjustable. You remove the valve covers and get one of those sets of oil shields that clip to the rockers that was made for the small block Chevy engines. If you don’t use these, oil will go everywhere.

With the clips on, start the engine. Then, one at a time, loosen each rocker until it starts clattering, then slowly tighten it down 1-1.5 turns. The engine will run quieter and have more power when you get done.

From the GM factory service manual for a 2004, 3.1 liter engine:

“Tighten the valve rocker arm bolts to 32 N-m (24 lb/ft).”


Haha i push return twice…on my phone it shows up spaced but smashes it all together when i post hahah.

Anyway… actually had time to mess with today. Pulled the motor forward to to crack open the valve cover. All the rockers were tight, no sticky valves… cranked the motor over and watched for any kind of unnatural movement…everything checked out fine.

I decided to change the plugs and wires while i had easy access to the rears… i was excited when i found a spark plug with a gap more than double spec…i though maybe the F’d up spark was causing piston slap or something… put it all back together and fired her up…immediately hear the same loud ticking/knocking. What a shame.

You could have easily checked for a stretched timing chain with the valve cover off.

You rotate the crankshaft in one direction to remove any slack from the timing chain. Then while watching the valve movement, you rotate the crankshaft in the opposite direction.

If the crankshaft can be rotated even a few degrees before there’s any valve movement, that’s an indication of a stretched timing chain.


I crapped the bed on that one! Ill pull the cover off and check it out if it comes down to it.
I will also add that the car began to run a bit rough while waiting for it to warm up to leave work yesterday… I goosed the throttle a little to see if it would even out…it revved up but stalled when it idled down. First time the car has ever stalled.

Well i took the car to a shop. The mechanic said it sounds like to him that a rocker arm bolt stripped out and that he’ll need $200 more to crack open the rear valve cover to see if thats what it is. Otherwise thinks its lower end noise which would in my mind ‘total’ the car.

I told them i will come pick the car up because im not paying $300 total for something i can do in 30mins and possibly not even be the issue.