08 Tribeca - Brief rattle during acceleration...

[mvbighead]

So my wife just mentioned this recently, and during our weekend grocery trips, I noticed it frequently. Basically, any time you accelerate when the car is at a very low RPM (idle?), there is a rattle that lasts about 1-3 seconds and then quickly subsides. Noise happens pretty much every time the throttle increases past idle initially, and does not return until the vehicle rests at idle again and then accelerates.

I suspect this is the idle arm pulley (tensioner pulley?), but was looking for confirmation.

2008 Subaru Tribeca, ~80k miles

 

[NutBucket]

Could it be a heat shield? Can you describe the rattle?

 

[mvbighead]

I don't really think it'd be the heat shield, but I could be wrong. The rattle only seems to occur when coming off of idle engine speed. It really only last a second or two, and then stops.

As for the rattle, it is very rapid. In that short period of time, there are a lot of 'clicks.' But it seems something disengages and the rattle starts and stops in the same period of time every time. No noise exists at any other engine speed which is why I doubt the heat shield is involved.

Hope that helps.

 

[ummduh]

Could be pre ignition, or detonation.

Usually sounds like shaking a tin can with marbles in it. Low engine speed/high load scenarios.

What octane fuel do you run now? I believe the b9 is turbo, yes? Try running the next grade up if you're not already using whatever is premium where you are.

 

[njmodi]

Could it be a heat shield? Can you describe the rattle?

+1 to something like this... I have a rattle on my 525i that shows up right around 1.5k RPMs and lasts maybe 1 second.. mostly shows up under light acceleration - it sounds like the underbody plastic engine shield or something resonating, at least I like believe that's all it is ...

 

[mvbighead]

Could be pre ignition, or detonation.

Usually sounds like shaking a tin can with marbles in it. Low engine speed/high load scenarios.

What octane fuel do you run now? I believe the b9 is turbo, yes? Try running the next grade up if you're not already using whatever is premium where you are.

No turbo. Just a 3.6, standard fuel, but we could try a step up.

 

[BigSmooth]

This is a long shot, but in my Forester, a clip holding a metal AC line behind the engine broke and the line was basically touching the engine firewall. When I accelerated from a stop, the vibration caused the AC line to rattle against the firewall. This did not happen at higher speeds, presumably because the engine did not vibrate the same way at different RPM. I simply wrapped the line in some spare hose that I had and it went away.

 

[Midwayman]

My wife's crv had something similar. It was the heat shield on the cat. I'd just lift the car and go check all your heat shield first.

 

[natto fire]

My wife's crv had something similar. It was the heat shield on the cat. I'd just lift the car and go check all your heat shield first.

Yep. My mom's 2012 Forester did this. A shop was trying to sell her a muffler, but she declined and asked me to take a look at it. The upper shield over the cat was loose.