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Discussion Starter #1
I've got a 2000 Outback wagon thats due for inspection soon and have been plagued by a unidentified noise for a few months. It came out of no where and I cannot pinpoint it. I have ridden in the back seat and listened as well as the hatch. I can tell its in the rear. it sounds like a loose bolt where the washer is rattling around at a high frequency... I have check for loose bolts. I described it below in the recommended form, Any additional question post them up, I want to find this gremlin.

A. When does the sound happen?

X When engine is running
_ When transmission is in some particular gear
_ When turning
X On throttle
_ When braking
_ Over bumps
_ In cold conditions
_ At speed - wind noise

Specifically under load between 3000-4500 RPM. Throttle above 50%

B. Where does the sound come from?

X Can't tell
_ Drivetrain
_ Suspension/wheels/brakes
_ Front
X Rear
_ Body

C. Does the sound vary with some condition?

X Engine/transmission rpm dependent
_ Wheel rpm dependent
_ Air speed/direction dependent
_ Varies according to some other condition

If I accelerate slow I don't hear it, but over 50% throttle it starts at 3000rpm and fades by 4500rpm. Intensity/ Speed increases based on throttle application such as 50% to 75% or WOT.


D. Is there a vibration associated with the noise?

_ Feel it through the floorpan or seat
_ Feel it through the steering wheel
_ Feel it through a pedal

It sounds like a vibration but no change in feel when it occurs.

E. Does it affect drive-ability? how? (Essay question, 2500 words or less)

No, Just randomly started a few months ago. I listened in on the fuel pump with the cover off, no additional noise. Have replaced an axle all rotors and pads all around, went on quiet and still are. All fluids have been replaced and maintained. Exhaust was inspected and gaskets replaced. I am beginning to think it is the evap system but I looked it over and felt the lines, everything seems intact and connected.
 

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Mine was a little oring type gasket in the exhaust joint between the Y pipe and the first cat. Cost me like $5 for the OEM gasket and a few bucks for new bolts - 10 minutes with a dremel cutting wheel and it was fixed.
 

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Discussion Starter #5
1. All exhaust gaskets have been replaced, I thought it may have been a pin hole leak that let just enough air through at those RPMs to whistle. I've inspected it all and cannot find any sign of a leak.

2. Exhaust heat shields were removed back to the cat. There are not any at the rear of the car where the noise seems to come from aside the metal tray between the exhaust and the driveshaft.

The boots on the endlinks are shot but I don't see why that would make a noise when it seems to be throttle/ rpm dependent.

3. I considered the muffler, although when I did the gaskets it didn't seem to rattle at all. I don't know how loud the car would be, but I may remove the muffler and take a test drive.

Thanks for the suggestions

Based on the dependence on engine rpm or volume of air let past the throttle, I was most inclined to think it was the exhaust. I feel confident that I can eliminate that as the culprit which is why I am thinking its the evap system. That or harmonics, but if its harmonics I still can't tell whats vibrating to make the noise.
 

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On my Outback the seam on the side of the muffler was leaking and causing a high pitched whistle that could espcially be heard at highway speeds. I filled it up with rtv sealant that has decreased the whistle sound alot but I will have to eventually replace it..
 

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This is pretty classic, consensus is usually the muffler or gasket right before it. My car does it, its harmless, and I strongly suspect the precise origin is a drain hole (normal thing in MANY mufflers) that rusts enough to enlarge and form suitably to cause the whistle. Maybe I'll get something to plug the drain hole and see if it goes away on mine.

Oh, and it can come and go, as it has on mine.
 

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Discussion Starter #8
Thanks guys, this sounds like what I should be looking for. Thanks for all the fast responses.

I'll follow up and see if that solved it.
 

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Discussion Starter #9
I took the muffler off and drove up the street, 1st the car is pretty quiet without a muffler, 2nd no ringing although there were some more vibrations.

I saw some visible rust on the seam along the muffler. I just put some jb weld to try and patch it for now. I saw that the exhaust flange is getting pretty rusty and it will probably need a new exhaust by next winter anyways.
 
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Justin V
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