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strange whirring noise when shut down

Discussion in 'A4/S4 forum(B5 Chassis)' started by mikeya4, May 13, 2009.

  1. mikeya4
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    mikeya4 Member

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    my 98 2.5 tdi makes a wierd noise when you turn it off, it sound like air pressure but it whirrs down? so difficult to explain but doesn't sound right, any ideas?
    cheers
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  2. impster
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    impster Member

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    my A4 1.9TDi does the same - I'm told it's the Aircon system?
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  3. mikeya4
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    mikeya4 Member

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    yeah probably right, it doesn't sound metallic so im not too worried just doesn't sound right
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  4. NHN
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    NHN Modmetractor

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    Has that engine got the secondary air pump fitted as I had that on my S3/4 & made strange noises at times.
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  5. impster
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    impster Member

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    I would guess the aircon system (having thought about it) as it changes low pressure gas into high pressure gas, so at any one time, whilst operating there are 2 diferent 'pressures' in the system maintained by a pump of sorts.
    On shutdown, as the pump is no longer turning, this pressure (i guess) equalises throughout the system, and that may be the noise that's heard?

    Only a guess mind, I could be completelly wrong.
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  6. mikeya4
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    mikeya4 Member

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    thanks for opinions, i've found out it doesn't do it on short trips only after the cars been running for a while, would the aircon thing still do it even though i don't use it?
    cheers
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  7. mikeya4
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    mikeya4 Member

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    also i don't know if it has a secondary pump but its quite a deep sound
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  8. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    mine gurgles when i stop, from the bulkhead area drivers side. Aircon is what causes mine. I wouldnt have thought a 98 had a secondary airpump. Maybe its just the viscous fan slowing down?
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  9. mikeya4
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    mikeya4 Member

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    yeah could be it does seem like its coming from the drivers side. i guess i will have to inspect a bit more
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  10. alex-qts
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    alex-qts Member

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    yeh mind does it too, 2000 quattro t sport, the noise seems to be coming from the drivers side, near to the windscreen wiper area, i looked and there seems to be some kind of preassure valves letting of a hissing sound. and the pipes (metal) are really cold, i think it might just be the air-con priming itself for when you use it. (it only hisses on long trips with mine too)
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  11. jcb
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    jcb Active Member

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    air con gas release when compressor shuts down
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  12. mikeya4
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    mikeya4 Member

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    I think i've found mine, as strange as it might seem, it was coming from the air filter housing, i've noticed someone has drilled the filter box, its definitely sounding like its from there, random
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