Strange noise on acceleration
 

Reading SDBsxtr's post on the 'faint knocking sound' prompted me to post this. Mine's a little different, but since he's already got people trying to diagnose strange sounds, it seemed like a good time to post this question.

Like SDBsxtr, I have an '01 (it's the 3.2).

The noise I'm trying to track down sounds a little like a few dice being gently rattled in a Yahtzee cup. Unlike his, I only notice it when starting to accelerate in 1st, then again accelerating in 2nd. It’s not there at idle, nor if the engine is revved but not under load. It’s subtle, but can be heard clearly when the engine access panel is removed. I removed the belt and the noise disappeared, even when accelerating in 1st and 2nd.

I suppose it may be power steering or A/C related? I replaced the water pump a couple months ago (OEM, from Sunset)---hopefully I didn't get a bad one. I know that putting a new belt on (which I did, with the WP) can sometime cause other things (pulleys, etc) to fail, but I would have expected more of a squealing kind of noise. That's not what I have.

Any ideas? :confused:

i get a slight clunk when i torque the engine from stop.

I know you say it goes away with the belt off, but check your heat shields on the exhaust system, we see a lot of cars with strange rattling noise on acceleration that were traced to loose shields, and once secured, the sounds vanish.

That is probably your motor mount telling you "it's time"...............

frodo, if you have not done it already tighten each spark plug, the noise it makes when one is loose is the last thing you would expect from a spark plug.

Doesn't sound like loose heat shield sounds that I've heard before, but that doesn't mean it couldn't be that. I suppose the reduced stress on the engine when the belt is removed might give rise to less torque-related movement, less vibration overall, and might account for the sound disappearing? I'll look for a possible culprit in that area, though it could be a challenge since, as I mentioned, it doesn't seem to happen except when the car is moving. (Might be tough to replicate on jack stands!)

If I see anything that has any possibility of being the problem, I'll wedge something in there, take it for a short spin and see if the noise is gone. Thanks!

Wow, that's a theory I hadn't expected to hear.

Guess I better start stretchin', limber up those stiff muscles, loosen up those creaky old joints, ready myself for the increasingly challenging role of contortionist, all in prepartion for attacking those plugs...makes me wish I had a '57 Chevy instead of a Box!

The only plugs that are a pain are the two most-front ones...

That's 33% of ALL of them!!! C'mon Randall...you're gettin' to be an old fart like some of the rest of us. Don't you feel my pain, even a little?? :rolleyes:

[QUOTE=Frodo;259389]
The noise I'm trying to track down sounds a little like a few dice being gently rattled in a Yahtzee cup. Unlike his, I only notice it when starting to accelerate in 1st, then again accelerating in 2nd. It’s not there at idle, nor if the engine is revved but not under load. It’s subtle, but can be heard clearly when the engine access panel is removed. I removed the belt and the noise disappeared, even when accelerating in 1st and 2nd.

How can the sound be a loose spark plug if the noise goes away when you remove the accessory belt and run the engine?:confused:

Check the belt pulley & tensioner bearings for play (up & down movement) and also (if you have a manual transmission car) the alternator clutch which is mounted inside the alternator pulley itself. These clutches can grumble (like mine did) or chirp if siezed. It can be removed from the alternator shaft with a special tool. Steptronic cars don't have these clutches fitted.....

Um, no. :ah:

[QUOTE=Steve Tinker;259455] Didn't feel any play in any of the pulleys, and they all seemed to turn smoothly. I guess I need to read up on the alternator clutch---don't have a good feel how that works, may need to look into that as well. If it is a problem with "accessories" (ie, those functions driven by the belt), would there be a problem waiting for awhile, to let it worsen a bit, so as to make the diagnosis easier? It would be easier to track down if it didn't only occur when the car was in gear and moving...

Frodo, I'll bet you I'm right, don't fret about the plugs, take the rear wheels off and go through the access ports, use an extention and a flex when needed, take your time. Be careful not to over tighten, snapping a plug top off that deep in the head will likely make you invent new cuss words.

Trust me, it's likely this issue, if you search there is a sound file for this I think Scoir (sorry if that's spelled wrong) posted it. To Steve, when Scoir told me about it I thought he was nuts too, that's all I can tell you. I think the high compression contributes to loosening the plugs, I chased the belts, pulley bearings and more, it was the plugs.

Oh, it's that Houston heat that keeps you loose and pain-free. Spend a few winters in grey, dreary, damp, slushy, snow-ridden NE Ohio. THEN you'll know what I'm talking about! :p

I can sing with you here, We set the snow record almost every year, last year was something stupid like 120". If that isn't enough, they mix salt and syrup derivatives for road salt. It sticks to line sets and everything else, ruins your car within five years. My P car of course was never in it.

Oh, I don't even pretend we can compete with you up-state New Yorkers...we can't. You guys, I'd bet, have people makin' a decent living just shoveling and snow-plowing out people's driveways! My back aches just thinkin' about it.

Frodo,

Here is my experience with the alternator clutch pulley if you haven't already seen this thread.

ddb

http://986forum.com/forums/performance-technical-chat/21779-clicking-noise-solved-alternator-pulley.html

ddb - Great DIY!! I'll have lots of beer and steaks when I do my clutch/ims/rms if you aren't busy...I can also detail your car :).

JFP, just changed mount last year. Tranny mount maybe?

Appreciate this is a very old thread, but did you ever identify the sound. I have something similar on mine. My exhaust sheilds are very loose so I am going to re-weld them up, but I swear my sounds comes from the transmission itself.