Can someone identify source of this sound ?

[x3L2004]

When I take off from rest I hear a chirping noise almost like a birds chirp and it gets faster and faster until it fades away completely as I reach a certain speed. What could this be ? Seems to me it's either a belt or wheel assembly related


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[bmwdirtracer]

You've related your sound to road speed, not engine speed. Is this correct? If it's road-speed related, rather than engine speed, forget about the pulleys, and focus on the drivetrain /wheels.

One man's bird chirp is another man's growl, but I'll stick with the description you've given. Best bet is to get the car up on a lift, and spin the wheels by hand, and if necessary, shut off the ASC/DSC, and drive the car in the air while listening for your chirp. You may have to stop one or two wheels to get the others to spin, by the way.

Chirping will often indicate something lightweight or with little load. Does the sound change with side-to-side loading changes (cornering)? Whether braking or accelerating?

[x3L2004]

Chris the sound does change when I turn and it also changes with road speed. I think it's my brakes man I went real fast and let the car decelerate and the sound was like something rubbing in the rear wheels.


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[bmwdirtracer]

Is the sound very high pitched, a spine tingling squeal? Is there any hint of growling?

I'm going to have to suggest that you get a good BMW tech, or very experienced owner/DIY guy to take a ride with you. With the information available, I can't tell you whether to look for a bad wheel bearing, or a bad u-joint at the rear of the driveshaft, or a brake backing plate with a rock caught in it, or an inside pad that's worn out, and rubbing metal on metal when cornering, because of missing anti-rattle clip and a rotor with a big ridge. Most likely, a quick ride would point the direction. Any chance you could post a video, with a camera aimed at where the sound's coming from? (Anyone you could put in the back seat for a quick drive?)

[Brownie1]

Is the sound very high pitched, a spine tingling squeal? Is there any hint of growling?

I'm going to have to suggest that you get a good BMW tech, or very experienced owner/DIY guy to take a ride with you. With the information available, I can't tell you whether to look for a bad wheel bearing, or a bad u-joint at the rear of the driveshaft, or a brake backing plate with a rock caught in it, or an inside pad that's worn out, and rubbing metal on metal when cornering, because of missing anti-rattle clip and a rotor with a big ridge. Most likely, a quick ride would point the direction. Any chance you could post a video, with a camera aimed at where the sound's coming from? (Anyone you could put in the back seat for a quick drive?)

I've had the same problem lately. But mine sounds like it's coming g from back of car. Mainly when accelerating hard. I'm definitely 'leaning toward the, u joint. Is that a difficult job on my 325 i

[MIKYZZ4]

Just a quick question, does this noise also appear at startup, while idling in park or neutral-or only upon takeoff, and varies with actual vehicle speed, not dependent on engine speed or rpm?

[x3L2004]

Just a quick question, does this noise also appear at startup, while idling in park or neutral-or only upon takeoff, and varies with actual vehicle speed, not dependent on engine speed or rpm?

It only starts chirping when I take off at around 15-20 km/h and increases in frequency up until 60km/h until it's so fast chirping it dies off completely or I can't hear it because of road and engine noise. It's very audible between 20-60 km/h speeds.

Also there is a back plate behind the rotor which my mechanic was struggling to straighten out last time I was at his shop when he was inspecting my brakes. He wasn't able straighten it out. Could it be this thing ?


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[MIKYZZ4]

Exactly the part I was going to recommend you focus on!

[ross1]

Dry universal joints in the drive shaft(not sure what type joints on this car)will make a sound you might describe as chirping. The pitch will increase with speed until it's "gone", too high for us to hear.

EDIT; "Also there is a back plate behind the rotor which my mechanic was struggling to straighten out last time I was at his shop when he was inspecting my brakes. He wasn't able straighten it out. Could it be this thing ?" Yes, likely the culprit

[bmwdirtracer]

For the backing plate: Take a long screwdriver, and place it just past the outside edge of the top of the rotor, where it will hit the thin metal backing plate. Now hit the butt of the screwdriver sharply with a hammer, a block of wood, or similar. Do this every few inches around the perimeter of the rotor, working from top to bottom. This works best when the car has that wheel jacked up, in the air, car in neutral, so you can spin the wheel and hear whether you've made the noise go away. (The wheel does not have to come off). I would say, however, that since you're hearing a pulsating sound, rather than a constant squeal, I personally doubt it's the backing plate.

Instead, just from a hunch, I think you'll either have a bad u-joint, or a bad wheelbearing.

The X-3 has a typical u-joint at the rear of the driveshaft, and I have seen them go bad. If you crawl under the car with a good flashlight and a big screwdriver, you can use the screwdriver to gently pry back the thin heat shield at the rear of the driveshaft, and look for red coloring on and around the u-joint. If you see any such color, that is rust, and the u-joint is bad. Unfortunately, they're not easily replaceable, and the correct fix calls for a remanufactured and rebalanced driveshaft.

The sound changing while cornering, however, points to a bad wheelbearing, especially if the sound disappears when cornering in one direction. A bad wheelbearing is best diagnosed with the car on a lift, being driven, while someone listens to the wheel carrier (upright) from the inside, with a stethoscope.....and compares the sound to the other side.

[x3L2004]

For the backing plate: Take a long screwdriver, and place it just past the outside edge of the top of the rotor, where it will hit the thin metal backing plate. Now hit the butt of the screwdriver sharply with a hammer, a block of wood, or similar. Do this every few inches around the perimeter of the rotor, working from top to bottom. This works best when the car has that wheel jacked up, in the air, car in neutral, so you can spin the wheel and hear whether you've made the noise go away. (The wheel does not have to come off). I would say, however, that since you're hearing a pulsating sound, rather than a constant squeal, I personally doubt it's the backing plate.

Instead, just from a hunch, I think you'll either have a bad u-joint, or a bad wheelbearing.

The X-3 has a typical u-joint at the rear of the driveshaft, and I have seen them go bad. If you crawl under the car with a good flashlight and a big screwdriver, you can use the screwdriver to gently pry back the thin heat shield at the rear of the driveshaft, and look for red coloring on and around the u-joint. If you see any such color, that is rust, and the u-joint is bad. Unfortunately, they're not easily replaceable, and the correct fix calls for a remanufactured and rebalanced driveshaft.

The sound changing while cornering, however, points to a bad wheelbearing, especially if the sound disappears when cornering in one direction. A bad wheelbearing is best diagnosed with the car on a lift, being driven, while someone listens to the wheel carrier (upright) from the inside, with a stethoscope.....and compares the sound to the other side.

Awesome thanks for the suggestions Chris.


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