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So this actually happend a couple months ago, the engine or the front part of the car started to have a wierd noise whenever you exceed aprox 60 km/h or 40 mph, this sounds like if a fan would be hitting a plastic rigid part, if i keep accelerating the noise becomes more strong and the frequency of the "fan hitting the plastic part" also increases.

Important notes

  • The noise disappears whenever you turn to the right
  • The noise also disappears or it's imperceptible when idleing

This might be also important, we usually don't use the manual gearbox but i remember giving it a try for a couple of days until it displayed a wierd message that said that only automatic mode was allowed or something like that, the alert disappeard and nowadays i can switch between manual gearbox and automatic with no problem and this seems not to affect the sound.

Been to a couple of mechanics but everyone of them had a different conclusion. I don't know much about cars so I don't know what to belive, because the repairs that they propose aren't cheap

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Get under the car on ramps or on a lift and look for a loose plastic shield. This could be the splash shield under the engine, part of a wheel well, a mud guard or any other thin, flexible plastic part. Be thorough and you'll find it. Try to physically bend all the thin plastic parts under the vehicle until you find the one that bends easily but really should not.

The part may be cracked or it may be missing one or more fasteners. When you drive fast enough, the wind catches the part and bends it onto a position that allows it to touch the ground or some portion of the drive train, possibly a wheel or tire. When you slow down, it snaps back to its normal position.

This happened to me once, but not on a BMW. It was maddening until I figured it out.

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  • You were actually right, the mud guard in the pilot side is completely loose, I'm almost sure this will be the cause, thanks a lot
    – Sosa
    Jul 28 at 16:10
  • @Sosa Glad to help. Your good description of the problem played a major part in solving the problem.
    – MTA
    Jul 28 at 16:57
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First of all, I apologize for writing this post instead of a comment (due to not having enough reputation).

In addition to the other responses, I'd like to mention that it's important to consider the fact that the noise decreases when turning to the right. Turning on the front axis causes a shift in weight and consequent compression on the left side. Anything related to this action could be the potential cause of the noise: damping, bearings, stabilizer, silent blocks, etc...

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