E46 330 Fuel Tank Straps Knocking Noise
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  1. #1
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    Fuel Tank Straps Knocking Noise

    Hi,

    Have been having an intermittent knocking from the rear of my car for a while.

    The knock is coming from beneath the rear offside passenger seat, where the base meets the seat back.

    The knock occurs only when I am changing from first to second, and from second to third gear. Happens when the forward motion
    of the car slows when you depress the clutch to change gear. When I change gear it sounds as if something is knocking against the underneath of the car.

    I have looked underneath the car but nothing obvious. Just had the car up on the ramp at my local garage and they reckon the fuel tank straps may need replacing
    as you can push the fuel tank up approx. 1/2 an inch. They have checked suspension and prop shaft but nothing obvious.

    Does anyone know if you should be able to push the fuel tank up, or should the tank not move when you push it?

    Don't want to fork out on new straps to find out they were ok.

    Any other suggestions regarding this knocking noise would be appreciated as it is really starting to bug me!

  2. #2
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    Does the knock sound the same whether you have an empty tank, or a full tank of petrol ?
    The fuel tank being loose sounds abit like they're clutching at straws.

    If your car is an early 2000 model, then i'd ask them to check for subframe tear !

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    Quote Originally Posted by Ferret View Post
    Does the knock sound the same whether you have an empty tank, or a full tank of petrol ?
    The fuel tank being loose sounds abit like they're clutching at straws.

    If your car is an early 2000 model, then i'd ask them to check for subframe tear !
    Like Ferret says, check for subframe tear - sounds like the symptoms that you are describing...

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  6. #4
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    Cheers for the responses.

    No logic to when it knocks and doesn't. Can happen with any tank level. However I have noticed that when it is wet it does not tend to do it, bizarre!

    When I first discovered the noise I checked out for the rear sub frame tear problem but could not see any tear. The knocking noise is also very light, more of a tapping.

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    Why not wedge something in the trank straps so as to make them tight to eliminate that?

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    Sounds to me like he is confusing RTAB knocking on the console because of the general area
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    Like the wedge idea!

    I've got some 5mm pvc at my work which I could cut into strips and use them as wedges.

    Ta

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    Quote Originally Posted by rac030275 View Post
    Like the wedge idea!

    I've got some 5mm pvc at my work which I could cut into strips and use them as wedges.

    Ta
    You are going to find straps is a red herring
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    AFAIK all 330's are post march 2000 when the subframe problem was AFAIK eliminated with normal use...

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    I don't reckon it's the straps as I could not get the tank to contact the underbody on the area where I think the noise is coming from.

    But if I try the wedge idea I would be able to rule the straps out.

    I have even had the back seats out and had someone else drive the car whilst I lay in the back like a moron to try and find the source of the noise!!!

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