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      04-05-2012, 11:16 AM   #1
singularity
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Question Exhaust leak or another "specialty"?

I was cruising in automatic Sport Plus mode yesterday and floored the pedal for 3 seconds in a very short tunnel. When I released I heard a loud explosion from the exhaust. Hadn't tried 'farting in a tunnel' before and don't plan to. After this I started paying attention to exhaust note with windows down and noticed something. 3rd gear @ 1500 RPM, floor the pedal to 3/4 and this is what happens:

Car starts accelerating with a low rumble and from about 2500 RPM I hear a rattling/tweeting air sound up until 4000 RPM, after that exhaust becomes too loud to hear anything else. It sounds like a high-pitch wind rattle 'twe-twe'twe', not a typical exhaust air leak 'pr-pr-pr'

The sound of turbo spool is different and has refined non-rattling 'swoosh' sound. Do other owners have this? What could it be?

Thanks for any advices
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      04-05-2012, 01:03 PM   #2
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I am pretty sure that is the turbo and the bypass mechanism for the excess boost when you cut the throttle.
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      04-05-2012, 01:59 PM   #3
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Quote:
Originally Posted by sparkyg View Post
I am pretty sure that is the turbo and the bypass mechanism for the excess boost when you cut the throttle.
Thanks for the reply. I forgot to mention that the 'wind rattle' seems to be coming from under the car, around rear-under. When idling and flooring the pedal I don't hear that sound.
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      04-05-2012, 05:20 PM   #4
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Quote:
Originally Posted by singularity View Post
Thanks for the reply. I forgot to mention that the 'wind rattle' seems to be coming from under the car, around rear-under. When idling and flooring the pedal I don't hear that sound.
I agree with Sparkyq probably the turbos or a mechanism working with them. I have 2 twin turbo cars and what you are stating sounds similar to what i hear when accelerating hard then immediately lifting. The sound from under the car could be because you are travelling at speed or if it is standing still could be an echo from the engine compartment working its way out and under the car.
The same type of sound comes from my 911 turbo and it sounds as if its coming from the side front as you know its a rear engine car. My wifes X5M sounds like it is coming from the rear.
I hope that helps.

Last edited by AM47; 04-05-2012 at 06:32 PM.. Reason: spelling
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      04-05-2012, 06:10 PM   #5
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Quote:
Originally Posted by AM47 View Post
I agree with Sparkyq probably the turbos or a mechanism working with them. I have 2 twin turbo cars and what you are stating sounds similar to what i hear when accelerating hard then immediately lifting. The sound from under the car could be because you are travelling at speed or if it is standing still could be an echo from the engine compartment working its way out and under the car.
The same type of sound comes from my 911 turbo and it sounds as if its coming from the side front as you know its a rear engine car. My wifes X5M sounds like it is comimg from the rear.
I hope that helps.
Thanks for the advice, this is my first turbo car and I was worried about different sounds. This will give me a peace of mind.
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      05-14-2012, 06:23 PM   #6
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I was at the dealership with this "leaking" air rattle problem while under throttle, it's best heard in 3rd and 4th gear at low RPMs. I wanted them to check the solution that user "burns all" suggested on another board, asked them to check "Loose pipe clip on induction system". They checked and said there was nothing wrong with it, but...


They said that there's a new campaign that popped up in their system and it's exactly about the induction system. He said that BMW admitted some unintended, factory-made holes in the air induction system which they recommend now to be closed with a special tool which they ordered.

BMW also mentioned that this defect not only can cause the rattle air sound that I noticed long ago, but can also cause a negative impact on car's air induction. Check your dealerships about this guys.
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