Disturbing noise when I accellarate (valves maybe?)

[DrivenDaily]

Iv got a QX4 thats got about 125k miles and everything seems to work fine. I replaced the water pump, thermostat and timing belt by myself, and I believe this odd noise i'm hearing has been happening ever since i had the car (purchased a year ago).

This noise could best be described as shaking uncooked rice in a tin can.. It sounds alot like noisy valves, but iv never heard them so loud and un-synchronized as I do with this noise.

Any thoughts/suggestions??

Thanks!

[ezb57e]

Loose heat shielding somewhere?

[DrivenDaily]

^^I dont think so, considering the noise is completely dependent on how hard i accelerate. If i'm going up a steep incline, I can always hear it pretty loud, but if i'm just cruising, i cant even hear it

[ezb57e]

Is it pre-ignition/spark knock?
Is the engine totally quiet at idle?
Hate to ask, but is it full of oil?
Sounds like spark knock due to the uphill/load triggering factor.
Do you use premium fuel?

[DrivenDaily]

I don't think its spark knock. I know its not the fuel i used, cause It only takes basic 87octane, and iv used premium before, makes no difference. Its quiet as can be when Im either cruising or stopped

[atraudes]

In regards to using premium, did you use it consistently for a while, or a tank here and there? I ask because I remember not seeing any difference until going through 3 or 4 tanks. Mine wasn't knocking with regular, but it was a bit noisier and didn't run quite as well.

I won't say rattling that bad isn't caused by the fuel grade you're using, but it's not at the top of my list of suspects. Engine knock due to low fuel grade is mostly inaudible.

Is the check engine or any other warning light on?

I strongly suspect a heat shield rattling, or something external of the like, especially if you're not noticing huge differences in engine performance. I had an exhaust heat shield loose on a previous car and it came and went depending on a variety of factors such as RPM and engine load.

I'd crawl under the car and start pulling on things to see if anything's loose, notably the catalytic converters. They're bolted directly to the exhaust manifolds, so pretty close to the engine. Pull the plastic rock guard off the bottom and make sure nothing's in there.

[zach7685]

I second the exhaust shield idea, Have someone rev it and climb underneath. Take a stick like object and poke the shield and see if the rattle stops. Could take a while to pinpoint be be careful as they are hot.

[DrivenDaily]

Thanks for the responses everyone!

I'm aware of the rattling noise that comes with a loose exhaust shield. Im certain its not that because like I said, this noise is consistent and speeds up as the engine (under load) speeds up. The noise comes from the engine bay. Perhaps its just the valves. I'm thinking I might just do a couple tanks of higher grade fuel to be sure, but Im almost positive any car that doesn't call for premium fuel will never EVER require premium fuel. I mean, as an engine wears, compression ratio decreases if anything, and this is the only factor that necessitates a higher octane rating.

[Buzzman]

What year is it, and which engine?

[mateen110]

Same exact sound/issue. For a minute I thought this was my old thread because you described it just like the sound im experiencing.

I'm fairly certain it is a loose heat shield somewhere, but I can't really find it. Below is my thread I posted earlier and you can check out the attached sound below. They way I described it was a loose screw is rattling around somewhere...

strange-rattle-noise-heard-occasionally ... 89945.html

If you find out the solution, please keep us updated. Would love to save a trip to the dealership