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2001 Z3 2.5i Mystery Noise

Discussion in 'E36/7 Z3 (1996-2002)' started by Woodyhfd, Nov 12, 2015.

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    Woodyhfd

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    I recently picked up a 2001 BMW Z3 2.5i. The car has 80,000 miles on it.The car is in absolutely beautiful condition and doesn't even look like it's been dirty, top or bottom.

    It's making a high pitched squeal from somewhere in the driveline. It starts right after I roll away from a stop. It doesn't seem to be related to road speed or engine rpm, and the pitch never changes. I can make it come or go with the throttle. It goes away when I am accelerating or under engine braking. It seems to be most prominent when the car is moving at steady speed.

    It will not do it when the car is parked. I've ruled out the throwout bearing, as it won't do it when the car is stopped. With the car parked, I can rev the engine in neutral, or with the clutch in or out. No noise at all.

    I thought I might have a rear brake pad hanging up, but I backed them off with a pry bar and it's still there. Applying the brakes while holding the throttle steady doesn't make it go away. I thought it might be the parking brake shoes dragging, but I backed the cables off completely and took it for a ride. Still there.

    I thought it might be a wheel bearing, though the wheels turn freely by hand and they don't feel sloppy.

    There doesn't seem to be any gear whine from the rear end and the car doesn't look like it was ever driven hard.

    When I'm driving the car, I can make the noise come and go on demand every time with the throttle. With the car stopped or rolling (with the clutch in, or clutch out in neutral), I cannot make the noise with the throttle. I've tried killing the engine at speed and it disappears immediately. It is independent of the brake pedal or handbrake.

    It seems to be completely dependent upon a complete connection between the gas pedal and the rear wheels. I'm still leaning toward a wheel bearing, though I suppose that it could be a pinion bearing or something in the rear axle shafts.

    I have addressed a number of maintenance items that I thought might be responsible. I have changed the driveshaft center bearing and flex disc, replaced the fuel filter (with its built in fuel pressure regulator), changed the rear differential fluid to Amsoil 75-140.

    What am I missing?

    View attachment 2001 View attachment 2001

    Attached Files:

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    KCuv

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    its not a wheel bearing if it doesn't change with the speed of the car.

    without hearing or seeing it, my best suggestion is that I would check the condition of and the tension on all belts.
    Is it more noticeable when you start cold, and fade a bit as the car warms?
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    Woodyhfd

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    I don't think it's a wheel bearing either, as the pitch doesn't change with speed and it does not change when cornering.

    No change whether the car is warm or cold.

    It's not a belt. It sounds like it's coming from the back half of the car.
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    charlson89

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    Is there any way you can get a sound clip of the noise? So the noise is only there in gear and cruising right? Any particular speeds it happens at?
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    Woodyhfd

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    I'm not sure if I can record it. It can happen at any speed. It is dependent on throttle input. Only when there is not a strong load.
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    charlson89

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    Have you had the vehicle driven with the wheels off the ground can you still hear the noise then?
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    Woodyhfd

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    Yes. I have had it up on the lift and run it through first and second gear. No noise.

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