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View Full Version : So, what is my car rattle?



Wade Lippman
05-17-2016, 2:02 PM
I have a 2011 Subaru Impreza with 30,000 miles. When I first turn it on it makes a pretty loud rattling noise. It goes away after about 3 minutes, but continues to rattle when I accelerate or go up a hill. That diminishes for the most part after another 5 minutes, but never goes away completely.

I am blaming it the exhaust system; the muffler is really rusty and that is where the noise "seems" to come from. Is that a fair assumption, or could it be something more serious>

Jim Koepke
05-17-2016, 2:37 PM
Can you hear the noise outside of the car while it is idling?

If so, you may be able to locate the noise by using a piece of wood pressed against the exhaust system components to find the point from which the noise emanates.

I do not know much about Subaru engines, but have had "rattle noise" caused by everything from sticky lifters and loose hardware to lousy low octane fuel.

I have also used dowels pressed against engine components with my ear at the other end to isolate the point from which a noise propagates.

jtk

George Bokros
05-17-2016, 3:04 PM
Could be that the media inside the catalytic converter are loose or the heat shield on the catalytic converter has a broken weld that holds it to the catalytic converter body.

Morey St. Denis
05-17-2016, 3:40 PM
With a 2012 Impreza Sport having twice that mileage in our household, I can suggest that if it's coming from under the hood, top end of the engine, it's most likely an idler pulley tensioning the serpentine belt. I first noticed an unusual chirping almost squealing noise coming from that mechanism within a month of the car being new. Also observed its erratic pivoting motion during most revolutions of the accessory power belt. Our lousy dealership elected to take no action despite several requests for attention. In our case, the worst of that noise diminishes once the engine warms up, but can readily be localized through use of a stethoscope. It's on my list of things to do this summer, although I have not firmly diagnosed if its more likely the idler bearing itself or the spring loaded pivot that provides take-up and regulated tension to the serpentine belt.

Wade Lippman
05-17-2016, 5:57 PM
The noise seems to be coming from the bottom of the car, perhaps a bit further back than the engine. Is that where the catalytic converter would be?

I have an appointment tomorrow.

I have a 7 year extended warranty; it excludes the exhaust system. Presumably the catalytic converter is part of the exhaust system.

George Bokros
05-17-2016, 6:16 PM
Yes the main catalytic converter would be back there. Yes the catalytic converter us in the exhaust system. Some pollution control items are covered for 24K miles and other components are covered for 80K miles.

Wade Lippman
05-17-2016, 6:40 PM
Yes the main catalytic converter would be back there. Yes the catalytic converter us in the exhaust system. Some pollution control items are covered for 24K miles and other components are covered for 80K miles.

My warranty booklet says the catalytic converter is covered for 8 years/80,000 miles. Thanks for pointing that out.
Oddly, the extended warranty specifically excludes them. Go figure.

Since the dealer will take me while to get to, I presume it is safe to drive with a rattling catalytic converter? (should the local guy say that's what it is...)

Malcolm Schweizer
05-17-2016, 10:11 PM
Sounds like exhaust based solely on the description. I would also check the motor mounts, which could be loose and causing the engine to move under torque. That could be the root cause and the exhaust rattle only a symptom. Just another thought.

Todd Willhoit
05-17-2016, 10:17 PM
Safe to drive if that is what it is. Eventually it will collapse on the inside and block nearly all exhaust flow resulting in zero ability to accelerate. (Major constipation.) My Chevy V8 has a cat on each side. I drove with a rattle for two weeks before one side collapsed. Even with one bank of cylinders breathing free, I could barely make it down my street.

Steve Peterson
05-18-2016, 12:43 AM
A cracked exhaust manifold can make a noise that goes away after the engine warms up a bit and the crack swells shut. It is sometimes easy to identify the noise that is directly related to the engine RPMs.

Steve

Jim Laumann
05-18-2016, 2:03 PM
Safe to drive if that is what it is. Eventually it will collapse on the inside and block nearly all exhaust flow resulting in zero ability to accelerate. (Major constipation.) My Chevy V8 has a cat on each side. I drove with a rattle for two weeks before one side collapsed. Even with one bank of cylinders breathing free, I could barely make it down my street.

I have a 97 Blazer w/ a 4.3 v6 - same thing happened to me. Replacement cost wasn't all that bad.

Wade Lippman
05-18-2016, 2:33 PM
Loose heat shield. $21 to fix with some clamps. Well, that wasn't so bad. Thanks for the help.

George Bokros
05-18-2016, 6:18 PM
Glad it was simple and reasonable to repair.