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Discussion Starter #1
Yet another mysterious engine sound diagnostic thread...

2006 outback 2.5 n/a 5 speed manual 132k miles

I’ve noticed a odd tick/ knock sound from the engine in the last few months after getting head gaskets & rear bearings done. Since the rear bearing had been on its way out for a long time, I can’t say exactly when the noise started.

Seems to be coming from the front of the engine on the drivers side, changes with engine rpm but not speed or gear. Only audible after the car has come to full temp for some time (such as after getting off the freeway on my commute). Also only audible when a light load is applied; letting off or getting on the accelerator seem to make it fade away.

I have no clue what this is, but I’m getting nervous it might be needing attention soon before developing into something more significant. I have a video with the noise but unable to post it here(?) so far... hopefully will get that up in a bit.

Any thoughts?
 

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So back to the shop- noise was diagnosed as likely coming from timing belt tensioner or pulley. Sucked it up and had them do full timing belt (water pump looked good so it was left in). Tech stated the tensioner was wobbly and tapping the block at idle.

Of course as soon as I’m driving home, I notice the noise still there; no change. Not sure how I’m going to approach this now... dumped too much $$ into this car already to walk away, but don’t want to hang onto it if there’s a issue looming with the motor. Just really wish I knew what this noise is...
 

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I don't hear anything except exhaust and wind noise in the video.

How loud is the ticking/knocking supposed to be? If it does it at idle, or even if it does it at higher rpms, if you can record it from under the hood that would help. You could get someone to work the throttle while you record.

If it is dependent on rolling or driving, then it may not be the engine at all. How old is the clutch set? Release bearing? When's the last time you changed the trans oil?

Another thing may be the AC compressor ticking. So does it do it with the AC off?
 

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FWIW - Bad fuel pressure damper perhaps? The device that attempts to dampen the pressure waves that are established in the fuel rail as the injectors open and close...

This was discussed in another thread. Google it. May be be the source of your "ticking" sound...
 

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Discussion Starter #6
I don't hear anything except exhaust and wind noise in the video.

How loud is the ticking/knocking supposed to be? If it does it at idle, or even if it does it at higher rpms, if you can record it from under the hood that would help. You could get someone to work the throttle while you record.

If it is dependent on rolling or driving, then it may not be the engine at all. How old is the clutch set? Release bearing? When's the last time you changed the trans oil?

Another thing may be the AC compressor ticking. So does it do it with the AC off?
Noise is only notable with around 20-25 % loads on the engine: haven’t heard any component of it at idle. Happens with AC on or off, full clutch replacement (wear components and hydraulics) back when The head gaskets were done.
Got back to the shop Friday; drove it with two techs listening before the one ( their master tech) heard it. He described it as a low end noise but not rod knock... noted that he’d seen cars over the years with similar noises that never developed into any issues. Since the noise is so subtle at this point (apparently I am just hyper aware of my car’s noises) he suggested keeping an eye on it, and not worrying about it unless the noise changes.
Have you ever run into benign noises like that before? I’d assume any looseness in the bottom end, no matter how slight, would just be the beginning of trouble?
 

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exhaust leak???? They moved the exhaust to change HGs. Could be a gasket, AF or O2 sensor not tightened all the way. I've had engines with exhaust leak at the sensors sound like a light tapping.

Shifter bushings
lower clutch shield loose
timing belt tensioner
timing belt idler pulley
harmonic balancer
valve maladjusted
Heat shield(s) - The ones on my Impreza sounded like a rod knocking. I took them off.

These are just some. If the knock is internal, you can ignore it until something breaks or verify for sure it's internal with a stethoscope and then rebuild the engine if it is; or replace it.
 

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Thanks for all the input- lots of stuff to look at this weekend now.

One other observation - I just noticed a pronounced uptick in an oil leak from the AVCS pressure switch on the drivers side of the engine. Easy enough fix there, but just wondered to myself if that could be causing some noise in the valve train? I’ll have to read up on that I guess.
 

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Thanks for all the input- lots of stuff to look at this weekend now.

One other observation - I just noticed a pronounced uptick in an oil leak from the AVCS pressure switch on the drivers side of the engine. Easy enough fix there, but just wondered to myself if that could be causing some noise in the valve train? I’ll have to read up on that I guess.
Yep.

If the OCV is leaking, there may be an issue with pressure supplied to the Cam Actuator. Same if the oil level is low or the oil condition is poor.
 
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