2001 BMW 325i Flapping sound

Have the brakes been checked? There is a sensor on the pads which is to make a scraping noise when the pads are due for replacement.

Does the sound change when you apply the brakes?

The flex plate is a flywheel between the engine and transmission. I have to be honest, I never heard of anyone adjusting one. It bolts into place and that's it. Does the sound stop or change pitch when the brakes are applied?

Jen, you feel the problem is in the rear. Are you able to safely lift the rear of the vehicle? If you can, safely place it on jack stands with both rear tires off the ground. (Please make sure it is secure and not going to fall off the jacks). This is a rear wheel drive vehicle, correct? It isn't AWD, correct? If it is rear wheel drive only, start the engine put your foot on the brakes and place it in drive. Slowly release the brake so the back wheels spin. You may want to have a friend doing this in the car so you can move around outside to listen for the noise. See if you are correct and if the sound is from the rear. When it is time to stop the wheels from spinning, stop them with the brakes and DO NOT just shift it into park while the wheels are still spinning.

If you can do that, let me know what you find. Also, see if the noise changes when the brakes are applied.

Joe

If it is a CI I believe it is rear wheel drive. The XI is the AWD. However, please confirm.

As far as the noise going away when you hit the brakes, it sounds like you have a rotor that is slightly warped. That is my first guess.

Jen:

Warped rotors are caused by heat. It is very common. What happens is the rotor (which is the round plate behind the tire) gets hot and is no longer true. It wobbles a little. It could be ever so slight and not seen by the naked eye. Even if it was bad, you wouldn't be able to see it. There are two options that can be done. If the present rotor is still thick enough to be cut, it can be trued up on a lathe. If they are too thin to cut, they would need replaced.

As far as what you mentioned, it sounds like you are looking at the rotors. It is common for them to have scratches in them just from normal use. Yes, what you said makes total sense.

As far as your mechanic, I would think he would question the rotors. Based on what you have told me, (the noise stops when you hit the brakes) tells me that the problem is brake related. If a rotor is warped, it could be rubbing against the brake shoes at its high point and then be away from the rotor on its low point. Thus, you hear the sound.

Think about it. The sound speeds up when you speed the car up. Therefore, it has to be something turning at the speed you are going.

Jen, I am not there to actually hear it, so at best, I can hope I'm giving you good info about your problem. Hang in there and let me know if you are able to do the test I described. Or, call your mechanic and ask if he can cut the rotors on the rear of the vehicle. It is usually a cheap job to do. I live in PA and would estimate 10.00 a rotor to cut and 30 minutes labor. It may be different based on where you live.

Let me know what you find. I want to get this fixed for you. Let me know if you have other questions.

Good luck, Jenn. I hope it takes care of the issue. Let me know what happens.

I knew it had to deal with your brakes in some way since you told me it stopped when you applied the brakes. Jen, I am so glad you got it fixed. See that, you had to tell the mechanic what to do. Lol

It has been a pleasure helping you. I will miss our long posts. Lol You take care of yourself and let me know if you ever have a question in the future.

Joe