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E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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Old 08-23-2005, 08:32 AM
schomer schomer is offline
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Location: Portland, Oregon, USA
Join Date: Aug 2005
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Mein Auto: 1999 323 Convertible
Humming Noise on Startup

Hello All,

I recently bought a 99 323 convertible and noticed that when I start it up, I can hear a humming noise for 30-60 seconds, then it stops. I don't know how to describe it. It sounds like a little motor of some sort behind the dash or under the hood.

Do you know if there is something that has to go through a startup when you turn the car on, which eventually shuts off?

Since I'm not familiar with this car yet, I'm wondering if this is a normal startup/warmup thing happening, or if it sounds like I need to get it checked out.

The climate control turns on everytime I start the car, even when I turned it off last time. Turning this off right away, after starting the car doesn't stop the humming from happening so it leads me to believe it is not the A/C or something doing the humming.

Thanks for any feedback.

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Old 08-23-2005, 02:06 PM
edubs edubs is offline
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Location: The Jersey Shore
Join Date: Apr 2005
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Mein Auto: 98 E36 323is
i had a truck and had the same thing happen... but only for like 5-10 seconds on startup.. im pretty sure its the altenator making that noise.. but i could be wrong
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Old 09-01-2005, 02:14 PM
schomer schomer is offline
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Location: Portland, Oregon, USA
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Mein Auto: 1999 323 Convertible
thanks for the feedback. i'm probably going to send this thing into the shop for an inspection. i'll ask them about the noise, and the alternator. thanks again.
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Old 09-02-2005, 10:32 AM
99flhr 99flhr is offline
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Mein Auto: 00 Z3 2.8
Are you sure it`s not the secondary air pump which is SUPPOSED to operate for a short time on startup?
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Old 09-05-2005, 01:47 PM
Silver328i Silver328i is offline
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Location: Eastern US - like PA?
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Mein Auto: 1998 328i W/M3 sport susp
Its that black electric motor/pump near the passenger firewall under the hood - it's some kind of emissions pump or something (what I read when I first got my car and looked it up to find out what the deal was with the humming). It usually only comes on when the engine is cold and has sat for a long time (overnight) without being started, and goes off after a minute or so. It has something to do with the catalytic coverter or Air Injection Reaction (AIR) or Exhaust Gas Recirculation (EGR) stuff.

Last edited by Silver328i; 09-05-2005 at 01:49 PM.
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