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      11-11-2019, 11:27 AM   #1
christofis135i
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2011 135i knock sound

Noticed this the other day while in a drive through. Car has a weird knock sound when I rev it just a tiny bit. I don't think it's a huge issue, but I have no idea what it could be. Anyone got any ideas?

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      11-12-2019, 12:36 PM   #2
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Bump, I need help lmao
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      11-12-2019, 03:27 PM   #3
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I can't hear much through my crappy laptop speakers. Some questions that the answers for might help others help you:

Does it change when you are driving / under load
With engine speed (assume this is yes)
Have you lifted the hood and listened around to isolate it to front / back / left / right
Does it sound like metal, plastic
Have you ever heard fuel injector noise or actual rod knock to compare to
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      11-12-2019, 08:25 PM   #4
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For under $10, get a mechanics stethascope, and have a friend rev the engine while you place the scope on various places around the engine bay (except anything rotating). Be careful, but it should help isolate where the noise is coming from. It could be many things. If it's coming from the lower half of the engine, it's probably more serious.

Let us know what you find out.
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      11-13-2019, 08:54 AM   #5
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It sounds turbo or pressure system related since it clicks right at the end of your rev, when you would expect the boost pressure to release.

Do you still have your exhaust flap connected on your exhaust? Kinda reminds me of that maybe closing at the end of your rev
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      11-13-2019, 04:32 PM   #6
christofis135i
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Quote:
Originally Posted by tracer bullet View Post
I can't hear much through my crappy laptop speakers. Some questions that the answers for might help others help you:

Does it change when you are driving / under load
With engine speed (assume this is yes)
Have you lifted the hood and listened around to isolate it to front / back / left / right
Does it sound like metal, plastic
Have you ever heard fuel injector noise or actual rod knock to compare to
Does not change when driving or under load. Have not had the time as it just snowed 7" and is 20° here. I have heard a rod knock and it's not continuous like those. It only happens when I make it happen. Sounds like metal.

Quote:
Originally Posted by dtla1 View Post
It sounds turbo or pressure system related since it clicks right at the end of your rev, when you would expect the boost pressure to release.

Do you still have your exhaust flap connected on your exhaust? Kinda reminds me of that maybe closing at the end of your rev
It's connected but MHD has the flap open. Could fully disconnect it if that's the issue.

Someone commented on the YouTube video that it could be the exhaust banging against something or a bad engine mount/exhaust hanger.
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      11-13-2019, 04:46 PM   #7
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Quote:
Originally Posted by christofis135i View Post
Does not change when driving or under load. Have not had the time as it just snowed 7" and is 20 here. I have heard a rod knock and it's not continuous like those. It only happens when I make it happen. Sounds like metal.


It's connected but MHD has the flap open. Could fully disconnect it if that's the issue.

Someone commented on the YouTube video that it could be the exhaust banging against something or a bad engine mount/exhaust hanger.
Good ideas from the YouTube comment as well. It's only at the end of the rev when you lift off so I could imagine enough movement there for something like that to cause a clicking noise.
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      12-11-2019, 03:03 PM   #8
christofis135i
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Just now getting the car back from the dealer. Noise is coming from inside my downpipe. Have the AR design catless so looks like I'll be dropping the mid section to see what's going on 🤷🏻*♂️ I'll keep this updated.
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