Strange sound. Can’t figure where it's coming from.

O

Ohioan

New member
2006 Z4 3.0si with 70K miles. Six-speed manual.

Last Friday I started it up and heard a strange noise while sitting there in neutral. Though I wouldn’t describe it as a "noise." More like a "tone." Like a resonance of some sort. It's not loud; it's rather faint. Sort of sounds like a car horn randomly going on and off at low volume.

It can be heard inside and outside the car. I can't determine where it's coming from, but it seems to be slightly louder near the rear of the car.

The tone does not care if the clutch is pushed in, or if it's in gear. It can definitely be heard when the engine is at idle. If I slowly increase RPM, the frequency of the tone does not change. And then it seems to go away when I rev it up past 1000 RPM or so.

I recorded the sound with my phone. Here it is (18 second 3gp file):

https://www.dropbox.com/s/aymy86gbcbfga1a/2006%20BMW%20Z4%20Mystery%20Sound.3gp?dl=0
 
Had a new noise in the back of the car at idle the other night and realized I had left a bunch of tool in the trunk. :oops:
 
Was that sound recorded outside the car or inside? Any louder in the engine bay?

First thing to do is eliminate any fans / vent servo motors, so see if you can hear anything with just the ignition on without the engine running.

If it seems louder towards the back of the car it could be something like the fuel pump.
 
Thanks for the replies.

ph001 said:
Was that sound recorded outside the car or inside? Any louder in the engine bay?
Click to expand...
I recorded it inside the car.

I popped open the hood and stuck my head in the engine compartment. I couldn't hear it; I could only hear the engine running.

ph001 said:
First thing to do is eliminate any fans / vent servo motors, so see if you can hear anything with just the ignition on without the engine running.
Click to expand...
Yesterday I turned the key to the on position (but did not start the car). Complete silence.

Just curious... with the key in the on position, but car not started, is power applied to the fuel pump?
 
Just curious... with the key in the on position, but car not started, is power applied to the fuel pump?
Click to expand...

IIRC from when I had my E85, yes as it primed, but it was more of a 'whir/whine' that only lasted a few seconds and was one pitch. Not like your recording
 
^^^^correct. The fuel pump only runs for a split second on ignition to build up pressure in the fuel rail.

When you start the car it then runs continuously.
 
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