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2009 Forester
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Discussion Starter · #1 ·
I'm driving a 2009 Forester with 87k miles on it. It's been making a rough, sometimes race car noise that I'm having a hard time diagnosing. The engine sounds only slightly rough on start-up, but really starts to make a race car-like, high-pitched sound from about 60kph on, peaking between 80kph & 90kph.

The sound is constant, not changing with any turns. It seems to come more from the front driver side. There's been no clanging or clicking, nor is there any shuddering sensation from the drivetrain.

Although I can feel a rougher than usual vibration through the gas pedal, it is also constant and doesn't get worse when braking. There's been no issues with power loss or overheating and although I have the impression that the car struggles a little more on the uphills since the sound began, my wife, who also drives it frequently, feels that there's been no change. If there has been any, suffice to say that it's slight.

So far, I've re-welded the shielding on the undercarriage, which I had first assumed were the cause, as they had taken several hard blows and come loose. This helped, but did not fix the root issue. I've looked for leaks in the the exhaust system, but found none. I propped the car up and shook on the tires, but I don't notice any clear play in them. The CV joints all look healthy, with nothing leaking. Nor have I noticed any other leaks.

The sound keeps making me think that the issue is engine or exhaust related, but maybe its something else? I'm pretty confused and would like to fix it before it turns into something worse. I'd prefer to have a better idea of what it could be, before bringing it into the shop, though.

Thanks in advance, for any and all advice!
 

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2015 Forester 2.5i Premium 6-speed manual
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177 Posts
What transmission do you have? What shielding did you need to re-weld and what were the sources of the hard blows? Did the noise appear after them?

In the meantime, check your spark plugs and wires. I have known spark plugs to be loose and leaking exhaust gases and even found out of their holes and still attach to the spark plug wires. Check your accessory belts for being loose. The belt(s) may only slip at higher RPM's leading to a "glazed belt" that slips even more over time before failing at some point. The sound of a slipping belt is a high pitch squeal that comes and goes depending on RPM /Road Speed.
 

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2009 Forester
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Discussion Starter · #3 ·
I have the 2.5X. The shielding was the exhaust heat shielding. Sorry for making that vague in my first post. The hard blows came from rocks on a (mostly) 4x4 track and from (and I am loathe to admit this) backing off a small cliff-like portion of a friend's irregularly-shaped driveway and becoming suspended on top of two cement flower pots and the sharp edge of a grassy incline. :-/

I'll check the plugs & wires - thanks for the tip! It doesn't sound like the belt, but I'll still check it. I replaced that just under 20k miles back and recall that high whine that it made.
Cheers!
 

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2015 Forester 2.5i Premium 6-speed manual
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You're Welcome!

Do you have a manual trans, or not?

What are the engine RPM's at the respect speeds of 60,80, and 90 kph when the noise occurs? What gear are you in at those respective speeds?

I would wear ear protection to attenuate the noise, but can you duplicate the sound in question at those respective road speed RPM's while stationary? And if you have a manual transmission, when in neutral and the clutch engaged? When in neutral with the clutch disengaged?

If you have an automatic, at the same respective RPM's, in Neutral and then in Park, while stationary, does the noise appear?
 

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2009 Forester
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Discussion Starter · #5 ·
I have automatic transmission and had been able to duplicate the noise at the respective speeds, although with less of a vibration through the acceleration pedal.

I went out and checked the spark plugs, wires and belts. The wires and belts showed no signs of wear and tear (wires and plugs replaced roughly 16k km back). The plugs appeared in good condition, so all I did in the end was to back them out and then thread them back in, kind of the mechanical equivalent of turning something off and then on again, I suppose.

This seemed to have an effect: I drove for 50km, only being able to get up to 80kph for a few minutes (I live in coastal Mexico - the road system here isn't really designed for speed). I didn't notice the high pitched noise at those speeds, nor the vibration that I had felt through the pedal. I want to say that I could feel a bit of the old roughness and noise from the engine during the last 20km or so of the ride, but I could also just be being a hypochondriac...

Wife and I are making a longer drive on a better highway on Friday, so we'll have a better opportunity to listen to it. But for now, maybe it was just that a spark plug was loose. I'll post again later!
 

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2015 Forester 2.5i Premium 6-speed manual
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This is a challenge.

You touched the spark plug wires and plugs and it got better to some degree. Interesting. I would carefully remove each spark plug wire, in turn, and completely and inspect all connections looking for evidence of shorting to ground (tiny burn marks). Try running the engine at night to see if there are any, even faint, arcs. You may have had a loose plug or wire, hard to tell from where I sit, but not obvious when you R&R the spark plugs. Test the wire(s) with a Volt Ohm Meter (VOM) for proper resistance and continuity. See the Subaru Service manual for specs. They can break internally and / or be separated from the spark plug connector, but look fine otherwise.

But something seems to have broken or come loose due to the rough roads you need to travel on. It maybe something not expected, or small and hard to find.
 

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2007 2.5XT Limited 4EAT
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Just some food for thought...have you ever replaced the alternator? Failing diodes in the rectifier bridge will make a very high pitched whine. This symptom is usually exacerbated under full fielding, i.e. under higher revs/load. Though this would not entirely explain the engine roughness. As @karlaudi mentioned a failing ignition component or ground could cause the roughness...and possibly the high pitched sound. The high voltage of the ignition system can certainly cause electrical interference if some of that juice is "leaking" so to speak, or rather inducing a high voltage field into one of the signal wires going to the ECU. It is possible though that the engine roughness and sound you are hearing are simultaneous yet independent of one another.
 
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