Humming noise at start up, anyone else get it?
 

On my 02 I notice that there is a deep humming noise upon start up that will last a minute or two. I thought it was especially evident when the engine is cold, but now that I reflect on it I'm thinking it comes up regardless.

Its not me or the passenger humming, so does anyone have an idea what this sound is, if its normal or something to look into?

Secondary air pump? Back of the engine compartment on the passenger side. Runs on cold start for up to 90 seconds.

Also check your power steering fluid level. It might be a bit low causing the pump to cavitate a bit but once it expands on heating it goes away. Admittedly a wild ass guess.

Guess not everyone has it then? Well, the car seems fine so I guess its not urgent, will ask the dealer next time it goes in I suppose (and I might as well check the power steering)

Thanks for trying to help

Val, I'm almost positive it's the SAP like Ron said...I had the same question after I owned my Coupe for a few months and finally noticed it...

It sounds like it's coming from right behind the glove compartment, which is where the SAP is (inside the engine bay in that little gasket-lined corner).

Mine makes the sound too. SAP sound from glovebox area = "they all do that".
(another description would be it sounds like a big PC cooling fan )

All E46s make this noise (and presumably any other car that uses M52/M54/S52/S54 engines) on cold start, and it's the SAP. You can feel it vibrating if you put your hand on it while it makes the noise.

Every 96 and newer bimmer I6's I've worked on has done it as well. SAP without doubt.

Thanks for the replies, it makes me feel better to know that its likely a normal thing.

By the by, it is a fairly loud sound, and I do not have the same thing on my 2000 328Ci.

Next cold start, open the hood and look in the compartment on the passenger side by the windshield. Put your hand on the pump and see if the noise goes away after 90 seconds.
There is also a fan in the DME enclosure which is located in the same compartment.

Just out of curiosity, what does the secondary air pump do?

Connect to:
http://www.unofficialbmw.com/images/...20Part%203.pdf

and check out page 68.

Must be the wrong attachment, Ron -- that one only goes to 59.

Should work now.