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General E46 Forum
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Old 06-26-2011, 08:06 PM   #1
clydesdale
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Air release sound on shut down of motor?? 330i

I believe it is something to do with the vacuum. I hear a motor turning inside the car and when the motor sound stops I hear an air release sound. Anybody know what this is? Thanks.
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Old 06-27-2011, 12:26 AM   #2
BMW_Stu
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im pretty sure thats normal. i remember my Camaro ALWAYS did it. i don't particularly remember it happening on the e46 but i never payed specific attention to it. ill listen out 4 it tomorrow.
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Old 06-27-2011, 12:41 AM   #3
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mine does that too, but i think cause of my intake
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Old 06-27-2011, 06:56 AM   #4
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OP,

Funny you mention this because I recently noticed this with my ZHP as well. Not sure what causes it but now that I'm aware of this it does happen every time I shut down my engine.
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Old 06-27-2011, 07:10 AM   #5
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How about air con pressure release?
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Old 06-27-2011, 07:25 AM   #6
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Mine do the same ...
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Old 06-27-2011, 08:24 AM   #7
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It seems to be a fairly normal occurrence. Some people say its the oil separator and some say its the ac compressor releasing pressure. Either way, i dont think its really harmful.

if it makes any difference, my noise was more noticeable with my CAI on, weird?
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Old 06-27-2011, 08:25 AM   #8
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It's normal. Do you have a cold air intake?
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Old 06-27-2011, 08:32 AM   #9
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i have the k&n short ram and it does the same thing, but it only started happening when i took my entire A.C. system
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Old 06-27-2011, 12:38 PM   #10
clydesdale
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It has the stock airbox, the a/c is already off, and it occurs probably about 5-10 seconds after the engine shuts off. You can hear an electrical motor running, like a HVAC vent is electronically closing and when that stops, you hear the air release.
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Old 06-27-2011, 12:43 PM   #11
///Miller325ci
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mine does it too... i think it could be the sound of the throttle body closing... that is why its more audible for those with air intakes
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Old 06-27-2011, 02:01 PM   #12
OrientBlau
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Its the vaccum pressure being released.
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Old 06-27-2011, 05:21 PM   #13
omarmarji
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Its the vaccum pressure being released.
yeah most likely you are right because the same time when i took out my a.c. i also fixed my vacuum leak and i guess thats the reason why im getting the sound cause its the pressure being released properly threw the intake.
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Old 06-27-2011, 11:13 PM   #14
Chris-alfonso
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It's normal and I think it becomes more nocitable when you have a CAI.
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Old 06-28-2011, 07:55 AM   #15
napaxcon
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yup that is normal. the air that gets sucked in while you drive cant just stay there. its even louder if you have a cai. also if anyone is wondering a slight whistle from a cai is normal to. it usually happens when you press the pedal down about 1/4 the way !
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Old 06-28-2011, 10:00 AM   #16
jdstrickland
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Quote:
Originally Posted by clydesdale View Post
I believe it is something to do with the vacuum. I hear a motor turning inside the car and when the motor sound stops I hear an air release sound. Anybody know what this is? Thanks.
Normal.
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Old 07-13-2011, 08:59 PM   #17
Sir Binkley
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On my 2004 330 whistle turned into squeal after car warmed up. Finally traced it down to gummed up oil separator valve & piping. Car was starved for air after it warmed up and was pulling air thru the crankcase seal. Easy way to tell was remove the oil cap and start it up. Whistle was immediately gone as vacuum had a new source of air. Gumming up condition is a known problem and BMW has a larger diameter oil dipstuck tube, insulated valve assembly etc. to fix it. Often caused by numerous short trips. 3.8 hrs of mechanic time & parts cost me $1,000 though.
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