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Message: <blockquote data-quote="saat" data-source="post: 102484" data-attributes="member: 77">If by "airplane sound" when you step on the accelerator, I assume you mean a background whine coming thru the speakers whose pitch rises and falls with engine RPM.  This would indicate that an electrical interference from the alternator or the car's power circuit on the signal side of your system.Any 2-bit installer should be able to locate the source and fix the problem or put in a capacitor to cure the whine.  The capacitor can even be home-made. Another source of the interference is usually as a result of running the signal cable very near a large electrical source or power cable.  As an example, in an E39,  the power cable runs from the engine alongside the driver side of the center tunnel to the battery in the back.  It is advisable to lay the signal cable the other side of the car or as far away as possible from the power cable.  The other alternative is to shield the entire signal circuit.Of course a faulty equipment e.g. HU or amp may also cause this.  This is easily checked by simple elimination.  A BMW is no more notorious as any other car when it comes to electrical interference.Frankly, in almost all cases, your installer should be able to fix it.</blockquote>