Knocking noise at idle

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Knocking noise at idle

Postby tksGTB » Fri Jul 21, 2017 8:33 pm

Hey guys I need your help. On the weekend my car just started making a knocking sound and it now somewhat sounds like a diesel. The sound can only be heard from inside the car when the doors are closed and above 1500rpm it stops. I can't hear or locate the sound from the outside. I took it to a mechanic who was said it was normal but I feel like there's more to it. Do you have any ideas or suggestions on what it could? Or maybe I'm just being paranoid.
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Re: Knocking noise at idle

Postby tom_kauf » Tue Jul 25, 2017 4:31 pm

Hi tksGTB, could you post a video? Eg just record on your phone and upload to YouTube. Otherwise it could be many things, so it's a bit hard to help without hearing it.
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Re: Knocking noise at idle

Postby tksGTB » Fri Aug 11, 2017 1:21 pm

hey tom_kauf i will record a video today and post it on youtube and then add it on here tonight. I still have no ideas what's wrong with it.
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Re: Knocking noise at idle

Postby tksGTB » Fri Aug 11, 2017 1:26 pm

https://www.youtube.com/watch?v=RoAhJ-RVBZc

You can barely hear the sound. It also fades as the car gets warmer
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Re: Knocking noise at idle

Postby tom_kauf » Fri Aug 11, 2017 7:01 pm

Thanks for the upload. It doesn't sound too different to my car to be honest.
Is your exhaust stock? All I hear is an exhaust rumble that may be a leak in the exhaust (or join between sections). Or just aftermarket mufflers - some types have packing that degrades over time, making them louder.

Since you mention it can only be heard inside the car, it might be in the front section of the exhaust - maybe at the dump pipe. My exhaust is stock except for the dump pipe, so it's a tiny bit louder than factory (but barely noticeable). So maybe that's why I think your car sounds like mine.

And it's not just on cold starts, or is it? Because the Secondary Air Pump, which is used for emissions makes the car sound like a diesel on cold starts. But only for the first 20sec or so.
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Re: Knocking noise at idle

Postby tksGTB » Fri Aug 11, 2017 8:11 pm

The exhaust is stock. The sound can be heard clearly on front passenger side of the transmission tunnel. As the cars gets warmer it's not as loud but I can still hear it.

Do you suggest I should get the exhaust checked?
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Re: Knocking noise at idle

Postby vinshonz » Sat Aug 12, 2017 2:45 pm

can you get a better recording of this sound?
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Re: Knocking noise at idle

Postby tom_kauf » Sat Aug 12, 2017 4:41 pm

tksGTB wrote:The exhaust is stock. The sound can be heard clearly on front passenger side of the transmission tunnel. As the cars gets warmer it's not as loud but I can still hear it.

Do you suggest I should get the exhaust checked?


Hmm, it's interesting that the sound is louder on the passenger side. Because the GT exhaust goes down the driver's side. But yeah, get it checked. Unless someone can suggest something else, I can only hear an exhaust rumble.
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Re: Knocking noise at idle

Postby tksGTB » Sun Aug 27, 2017 5:32 pm

tom_kauf wrote:
tksGTB wrote:The exhaust is stock. The sound can be heard clearly on front passenger side of the transmission tunnel. As the cars gets warmer it's not as loud but I can still hear it.

Do you suggest I should get the exhaust checked?


Hmm, it's interesting that the sound is louder on the passenger side. Because the GT exhaust goes down the driver's side. But yeah, get it checked. Unless someone can suggest something else, I can only hear an exhaust rumble.



I will be getting it checked when the airbag gets replaced. Thanks very much for your help. I know its really hard to hear it from the video.
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Re: Knocking noise at idle

Postby Cam_Haug » Tue Sep 18, 2018 9:05 am

I know this post is pretty old, but both my foz and my lib do this, I THINK it is the fuel system pulsing (fuel lines run down the passenger side, its really noticeable getting off light throttle coming to a stop. I managed to make the forrester a bit quieter by replacing one of the fuel dampers but it is still there.

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Re: Knocking noise at idle

Postby MY02B4 » Fri Jul 12, 2019 5:16 pm

Anyone else have this issue?

I'm hearing the same thing inside my 2.5t Lib. It's much more audible inside the car around the front passenger side. I almost cant hear it when I stick my head under the car around the area and cant hear it at all in thr engine bay. The noise doesnt go away when the car is warm and I havent noticed much difference in performance altough I am reluctant to floor it too much.

I've already bought all the parts for my timing belt service so I might book it in earlier for peace of mind.
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Re: Knocking noise at idle

Postby bigBADbenny » Fri Jul 12, 2019 7:08 pm

Depends on your mileage, probably just valve noise/clearances, or maybe a heat shield on the turbo or exhaust.
Next time the car is on a hoist tap all the shields to see if they’re loose or ring.

And check your oil level, mine needs topping up monthly, probably valve seals or oil control rings lol
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Re: Knocking noise at idle

Postby MY02B4 » Fri Jul 12, 2019 9:01 pm

Hey BBB long time no chat!

Oil was a tad low so i topped it up. I reckon its an exhaust leak on the top side which explains why its louder along the passenger side floor than under the car or inside the engine bay.
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Re: Knocking noise at idle

Postby bigBADbenny » Sat Jul 13, 2019 7:39 am

Did I buy your Perrin tmic back in the day? :P

I can Lv your car, log it if you have an android...

Or log n Lv if I break out the laptop :)
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Re: Knocking noise at idle

Postby MY02B4 » Sun Jul 14, 2019 11:03 am

I think i bought the Perrin off you or maybe it was the AVO and you threw in a Crumpler bag. It was ages ago and I'm confused with the PMs because there were msgs about whiteline gear, bent K2 tips etc. I've got a Android. What else do I need?
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