840ci - An electrics question, if someone can help..

    I've made some further discoveries about this issue, (Sandwich will be thrilled to hear).


    Firstly, Revtor: Funny you made a minor disclaimer after your initial reply, because your instinct was completely correct. You're so money! (which I believe is contemporary parlance of the street, meaning 'bravo' or words to that effect).


    Tonigh i went via some quiet roads home so I could isolate this noise better.
    When lights are on, or on halfway, its constant .. is almost singular in tone but has a slight resonating aspect. Very hard to tell where its coming from, but more on that in a minute.
    If you turn the lights completely off, it stops sharply, then starts up again approx 5 seconds after putting lights back on.
    As said before, i always have my instrument brightness fader up full, but mindful of Revtors words I tried fading it.
    Hey presto.
    The noise diminishes by an exact ratio, depending on how faded or bright I want my instruments.
    Very bright, its noticeable. Halfway bright, its still noticeable but much less so. Turned almost right down, the noise is pretty much gone though still (just) detectable. Therefore, this is a situation I could ignore by just keeping instruments dim.
    I'd prefer not to do that, and wonder if anyone recognises this symptom.. or has a suggestion to make.
    Lastly, I spent a good while determining source of sound, and as close as damn found it! Sitting in normal position - if you crane your neck and put your ear next to the air vent to the immediate left of my (RHD) steering wheel - the noise is way easier to hear. Almost emanating from the airvent.


    I tried pressing ear to other vents/ gaps etc but it was loudest from that airvent. Whatever makes the noise is behind it, no idea how far though, it echoes a little :driver:

    BBMatic: Did you also put your ear on the dimmer? Is the noise clearly stronger around the center vents than the dimmer? It's now clear the noise is caused by the dimmer, but it may not be the dimmer itself emitting the whine.


    The only thing behind the center vent that is related to the dimmer is the single light bulb that illuminates the center vent roller wheels. Incandescent light bulbs can make a noise when dimmed. The switched current through its filament makes it vibrate. The filament noise is more towards a ringing sound than a whine/squeal. Is that what you mean by "slight resonating aspect"? I must admit, though, I never thought bulbs as small as the one in the center vent could make audible noise. I'm still confused as to why the noise gets softer when you dim the instrument lights more. From my experience with dimmers and dimmed light bulbs, the noise should always go down with increasing duty cycle (brightness)...


    It would be interesting to find out what happens when you remove the center vent light bulb, but that piece is very hard to remove and prone to breaking. A replacement center vent will set you back over 500 EUR (not a typo), so you should be very careful with it... Sadly you can't reach the bulb from the radio/MID opening.

    Zitat von revtor;97715

    BBMatic: Did you also put your ear on the dimmer? Is the noise clearly stronger around the center vents than the dimmer? It's now clear the noise is caused by the dimmer, but it may not be the dimmer itself emitting the whine.


    The only thing behind the center vent that is related to the dimmer is the single light bulb that illuminates the center vent roller wheels. Incandescent light bulbs can make a noise when dimmed. The switched current through its filament makes it vibrate. The filament noise is more towards a ringing sound than a whine/squeal. Is that what you mean by "slight resonating aspect"? I must admit, though, I never thought bulbs as small as the one in the center vent could make audible noise. I'm still confused as to why the noise gets softer when you dim the instrument lights more. From my experience with dimmers and dimmed light bulbs, the noise should always go down with increasing duty cycle (brightness)...


    It would be interesting to find out what happens when you remove the center vent light bulb, but that piece is very hard to remove and prone to breaking. A replacement center vent will set you back over 500 EUR (not a typo), so you should be very careful with it... Sadly you can't reach the bulb from the radio/MID opening.


    Revtor [ and Reinhard for that matter] Have either of you TOTALLY dismantled an 8? Just wondered! In awe......

    Quick reply:
    Revtor: It is more of a ringing noise than anything - sorry , I didn't mean to suggest it was a whining noise.
    As it happens I didn't glue ear to the dimmer because the noise was clearly loudest from that vent on the other side - hence i focussed on that side - however i will check on the other side too.
    Definitely no mistake about it, the brighter the dimmer, the louder the ringing noise.

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