Strange High Pitch noise seems to be coming from rear (4.8is) - any idea's???

[Lion Heart]

Hi guys

Recently picked up a 4.8is!!!

It has a couple of niggles which I need to iron out, which is not an issue as bought it quite cheaply and will be a cracker once done.

My first issue is a strange, high pitched permanent noise which seems to come from towards the rear of the car. Seems loudest around the rear wheel area.

I thought first of all maybe an exhaust leak, but if you do anything electrical then the pitch of the noise changes, so definitely electrical in nature.

I've taken a video (27 seconds). Have a look:

https://www.dropbox.com/s/b0ua362zw8...N2720.AVI?dl=0

In my video you will note I whistle at the start to mimic and help you hear the noise I am talking about - and as you will see when I push the rear window switch you can hear the pitch changing - nence pretty sure it must be electrical!

Surely they can't all make this noise!?!?!

Any help really appreciated as it's really annoying!!!

Thanks guys!

[LVR]

Hi,

I would have a look at the window lifting motor. See if you can isolate the sound to the door and if so open up the door and check it...

[Lion Heart]

Pretty sure that won't be it. Just used the window switch as an example. The noise changes whenever you do anything electrically orientated.

It's as though something is taking a charge and making he noise, and when you direct power anywhere else it drop the power a little to whatever makes the noise and so the tone changes a bit.

Any ideas???

[upallnight]

Could be the electrical fuel pump. I would take an amp clamp and see what type of amp the fuel pump is drawing. The fact that the window motor is affecting the fuel pump leads me to think that the fuel pump is drawing too much amp. Another expensive fix.

[Lion Heart]

If it is the fuel pump drawing too much power, would that mean a new fuel pump needed?

Are they big money??

[Lion Heart]

If it was the fuel pump wouldn't you be able to hear it inside the car as it's located under the rear setas?

If you close the door you don't really ear it anymore...

[wpoll]

Originally Posted by Lion Heart

If it was the fuel pump wouldn't you be able to hear it inside the car as it's located under the rear setas?

If you close the door you don't really ear it anymore...

Easy enough to eliminate the fuel pump - unplug it and see if the noise goes away. That is assuming it makes the noise with just the ignition on and the engine not running.... as it'll be hard to run the engine with the fuel pump unplugged!

There's not much else back there that could make a noise like this - or at least not much that isn't inside the car. The audio and nav systems are inside, along with the compressor. The diesel has an extra in-line fuel pump in the fuel line under the car but I don't see that on the 4.8is.

I guess it could be a bad audible oscillation in and ABS wheel speed sensor or a parking sensor but I'm thinking that would show

up in other ways, like ABS lights on the dash at the very least!).

I don't recall seeing in any of your threads you saying that you have scanned the car for codes... might turn up something.

[upallnight]

Originally Posted by Lion Heart

If it was the fuel pump wouldn't you be able to hear it inside the car as it's located under the rear setas?

If you close the door you don't really ear it anymore...

If you remove the seat and all the sound insulation from the back you will hear it.

[Lion Heart]

Hi guys!

Ok, so following up on this...

I mnaged to get the car on a ramp, went underneath with the engine running and the high pitched noise definitely seemed to be coming from the bottom of the fuel tank area. And it was also accompanied by a grinding/scratching kind of noise as well.

So, my thoughts get the fuel pump changed ASAP.

So fitted a brand new fuel pump (not too bad a job to do to be fair). The high pitched noise has now gone (hooray!) but that grinding/scratching noise is still there and does not sound very nice.

You do need to be close to the underside of the fuel tank to hear it, you cannot hear it inside or outside the car AT ALL unless you're within a few inches of the underside of the fuel tank.

I've taken a video and would really welcome some opinions on it...

https://www.dropbox.com/s/mk41qg13ana8w4h/BMW%20X5%20Fuel%20Tank%20Scratching%20Grinding%20N oise.mp4?dl=0

You can hear it quite clearly grinding/scratching when I zoom in close to the bottom of the tank.

Now, that's a brand new fuel pump and it did this same noise before and after the pump change, so I would think it must be something else? Is this noise normal?????

[jopecasa]

Check Battery grounding cable........seems like a ground loop!

Or do a double run of earth cabling from battery on another earthing point.