Fuel pump - not the HP one

[Z4 Beemer]

For about a month I've noticed if the fuel tank level is somewhere other than max or min there's a sort of knocking/tapping noise, almost like a kettle boiling (fuel bubbling noise). You can hear it at idle with the radio off. You hear it over your right shoulder, and I'm pretty sure its coming from the fuel tank/filler area. Pretty sure not an exhaust rattle, or coming from the engine, but I had wondered if it was related to the fuel return valve...?

Saw this thread on a rival forum this morning:

http://e89.zpost.com/forums/showthread.php?t=516363

You really do need to turn the radio and heater fans off to hear, but there is something definitely there. It isn't affecting engine smoothness/idle/performance in any way, and the level of the noise definitely depends on how much fuel is in the tank. I filled the tank fully last night and the noise has gone, but when the fuel level starts dropping, I am expecting the noise to return again.

Anybody else notice this?

[Z4 Beemer]

Right, I asked them to look at this yesterday when it was in for the bumper vent recall and oil and brake fluid change.

I left them the following note:

Knocking/tapping noise coming from behind drivers seat (noticeable over right shoulder) when fuel level is between 1/4 and 3/4 full and car at idle. Noise starts straight away after engine started from cold, and remains constant. Level of noise depends on amount of fuel in tank. Full tank of fuel causes noise to disappear, but starts becoming noticeable when fuel level drops.
Pretty sure not exhaust or from engine, so could it be from the fuel tank - fuel pump maybe?

Apparently there is a technical bulletin to do with this... the service adviser said I could have written it myself, as I was describing it exactly! Its something to do with a flap, return valve type thing that knocks in the tank, and nothing to worry about! I think because of reduced sound deadening and sitting so close to the back of the car, noises like this will be transmitted into the cabin.

[ksher]

Will BMW replace the low pressure fuel pump (LPFP) in the fuel tank to fix the knocking noise?

You made me worrying now. The tank is now half full, so I will check it when I'm driving home after work.

[Z4 Beemer]

Definitely not the pump! They mentioned flap / return valve thingy that's making the noise, but you only hear when fuel level is between certain ranges (I reckoned 1/4 to 3/4). I think any fuel that is not used is returned to the tank... and that's what is making the noise.

Didn't get to see the bulletin though.

No need to worry!

[ksher]

I read the posts from your link above, and the 23i/30i owners had LPFP replaced due to the noise. Was it a different issue?

[Z4 Beemer]

Hmmm - wouldn't describe the noise I hear as a "humming" noise, really more of a knocking/tapping. I think if the fuel pump is on the way out, the idle would suffer as well as there being starting difficulties (long turnover). I haven't seen any of these symptoms.

Seriously, it seems there is no need to worry!

[shambolic]

As I said same noise from my SLK