E36 Coupe window problems

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HI Yeah i'd love to be able to help. I.d like to say, i've had the same problem. Not all the time but still occures when it feels like it!
Any help would be appreiciated.
Someone mentioned to me about the alternator producing to much valtage can make strange this happen to your car. If i shut the door when the engine is running it will make the revs lower briefly?? what causes that??
Im lost for ideas. Any help appreiciated as i said..