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Metallic rattling noise

My '99 Legacy is far from quiet, but yesterday I heard a new – and somewhat alarming – noise.

Roughly two-thirds of the way through a four-hour drive, I started to hear a rattling or grinding sound coming from the front of the car, perhaps closer to the driver’s side than the passenger’s. It sounded as if a tin soup can or paint can were hitting the road, but when I popped my head under the car, nothing was hanging loose.

I hear the rattling sound as I begin to accelerate, and only when I have my foot on the gas – when I let off, it’s perfectly quiet. What I haven’t been able to determine is whether the noise goes away after I reach a higher speed, or whether the sound of the usually loud engine drowns it out. The noise is most acute around 1500-2000 rpm whether it’s in gear, or whether it’s in neutral and I’m revving the engine.

Any thoughts on what this might be? It would be greatly appreciated!

A heat shield on the exhaust system broke loose or rusted off. Unless you make a habit of parking on dry grass or other flammable materials, just break it the rest of the way off and drive on.

+1 on the heat shields. It is a common Subaru thing to have happen. It isn’t serious but just annoying. It sounds like something really bad is happening - but you’re likely okay.
Look behind the bumper, towards the front of the engine where the exhaust manifold bolts onto the engine. You’ll note that they have tin covers on them, one on each manifold. One of both are probably kinda loose and resonate with engine speed.
Go to HomeDepot and buy some large band clamps* and wrap them strategically around the offending heat shield.

*like this but larger: http://www.pipe-clamps.com/productsimages/12mmbandclamp_164865.jpg

So the heat shield would only rattle while accelerating? Not while coasting?

Thanks for your prompt and thorough responses!

As the engine twists under acceleration it moves the exhaust pipe and the pipe comes into contact with the heat shield. When you stop accelerating the engine stops twisting and the pipe moves away from the shield.

Yup.
That, and is is likely resonant with a certain vibration. You may get it to do it at a certain engine speed, without having to be in drive. Start the car, get it to the speed where you near the noise, have your wife hold it there and you - very carefully* - look under the car towards the front. You’ll likely be able to stop the rattle by just pressing on it with a screw driver.

  • if your wife likes shopping and your life insurance policy is huge, maybe have a neighbor do it instead.
    j/k.

When I hear “mettaly rattling noise” I always wonder of it isn’t pingiong you’re hearing. Have you any fault codes stored in the ECU?

I’ve fixed a few rattling heat shields exactly as Remco describes, but be sure you’re not hearing pinging.

Look at the flex pipe from the engine to the rest of the exhaust system. These flex pipes have a flange that can rust off the flex pipe where now it just rides on the pipe and makes ringing noise as it vibrates up and down the pipe.

Tester

Probably a heat shield, but it could be any broken hanger letting a pipe oy muffler hit something upon acceleration.

I got under that car last night and, sure enough, a hose clamp around a heat shield – just like the one Remco illustrated! – appeared loose. When I gave it a little tap, a rusty bolt fell squarely into my palm.

Thanks to everyone for your input. As soon as I can, I’ll pick up a new clamp and have this car sounding (slightly) less noisy!

Ah, someone already tried to fix it with a hose clamp. It is certainly not a ‘dealer installed anti rattle option’ - it is more a ‘redneck stop-the-noise fix’.
Good. Glad it isn’t anything serious. Hose clamps are cheap.

I had a similar experience with my 2001 Tahoe was making a noice by the driver side and it was a heat shield making the noises