What is the low-pitch quiet rumbling in the trunk area after startup?
 

Noise seems to stop after a minute or so.

Only a couple of things moving in that area -

Fuel pump - sound would be center, behind rear seat;

CD changer - could it be the changer booting and spinning up a CD - would be left side of trunk.

Power antenna... right side of trunk - is the stereo turned on and you're hearing the antenna raising (or trying to unsuccessfully if you don't see it coming up, until it times out). Turn it off and see if you hear the same sound from it going down again (or trying to).

Thanks, I have no directional concept since I hear it from the drivers seat - basically, this is nothing to be concerned over, right? Fuel pump is normally noisy and so is the CD changer (definitely not antenna, distinctive sound and happens with radio off), nothing else would make such a low-pitch grumble from the rear, right?

Sounds like it could be a CD changer sound, going to try to remove the cartridge and see if the car still does it.

I have the same noise but if I blip the throttle it normally goes. :)

Maybe some fault in the exhaust system - maybe a hanger broken or insulator cracked? If you can get the rear of the car up on ramps and goose the engine while someone listens (but not underneath!!!) it can be localized.

I guess the next question is - does it make the noise only with engine running, or also when key is just placed in run position, without starting the engine?

The two related to stereo would occur in either case. The fuel pump only for a couple of seconds if the engine is not started.

My car occasionally makes a low pitching buzzing noise in the rear for about 3 seconds after start up. It occurs when I do a warm start (car is parked for between 30 mins - a couple of hours). No noise at all on cold or hot starts. Its done this for 7 years and 50k miles. My engine makes a sort of a burbling noise and gets somewhat close to stalling until the ECU picks up the idle speed when this occurs (it doesn't stall though).

A bit of throttle while starting prevents this noise.

Rumble from back seat area on starting
 

My 2002 xj8 ( 92k) has been doing this rumbling off and on both before I had a new pump and since. As you say, not when cold or hot, only when left for 30 mins or so. Only difference is today when the car started the idle sounded like if I pressed the throttle she might cut out. Then it seemed to sort itself out. Is there "trouble ahead"? Worrying till I read your post.

ref teejay246 - mine does the exact same thing - but only on a warm start after 20 - 60 minutes stop. It sounds like distant thunder is all I can describe it as. I'm sure its the fuel system at the back (I have no CD player for some reason). Its like the pump is drawing in some air or something. The noise lasts about 5 seconds then all is well. Been doing this for a year now and still not sure whats causing it...
The pump itself seems ok, it will start humming sometimes after a long haul but the car performs well and the idle seems ok.

In a nutshell - f*** knows !

AndyP

It's been doing that now for 4.5 years without any issue or concern until yesterday.

While running errands doing several warm starts the noise after start up increased in volume to what sounded like a low flying airplane overhead. There is also a much quieter but distinctive slight gurgling sound, almost like air bubbles being purged out of a hose of liquid. After about 5-10 seconds it stops and all is normal again.

What's causing this? Could it be contaminated gasoline or a clogged fuel filter? As long as it's just sounds I don't really care, but it would be terrible if this is a symptom that the fuel pump is beginning to fail.

The gurgling noise is from the fuel pump(s). It's like as if when the car is shut off, the fuel that's in the return pipe to the tank somehow manages to all flow into the tank and leave air in that return pipe. (I'm sure that's not possible) And then upon restart sometime later in the day, it sounds like it's purging the air out of that return pipe. I think the noise is more prone to happening with the fuel level under half full. I will have to pay more attention to this. Is this cause for alarm or should I replace the fuel pump(s)?? No.

As far as the thunderous noise as described, I believe this to be prone when the car has sat overnight and when first started is the resonation coming from the 'cold or ambient' exhaust. I can hear it more when you start it inside a small garage.

Thanks for the reassurance :) it went away by itself, although has done it just once again on a cold start in the morning. Previously it was always on warm starts - so apparently that is not a relevant factor.

The airplane-like noise has nothing to do with being indoors as it is similarly audible regardless (I've heard it both in a garage and outside, sounds the same because the noise is coming from behind the backseats through the car interior - it is quite loud)

.

I think I identified the trend, it seems to happen after filing the tank after being very low on gas (like 1/8 tank), does that info help identify anything?

Charcoal canister, evap system?


Are you having trouble putting petrol in the tank?

Pretty sure it is just the fuel pump. Both of my Xj8s make that noise. Also the radio antenna extending, sometimes.

Way louder than the a antenna extending! Like an airplane passing overhead...

Petrol goes on fine, but regularly doesn't trigger the pumps full-stop until the very last moment, splashing a few drops of fuel onto the attendant (they love that...)

Interesting. So has it gotten louder in the last five years? Pretty sure it's the fuel pump. But mine is not that loud; but does quiet down after about 10 seconds. Was a little louder before I changed the fuel filter.

I bookmarked this a long time ago and just kind of following up. I found a couple other related threads that also end without resolution, everyone just living with it. Just wondering if anyone ever figured out something to do to fix this? I've been living with it too but its kind of getting old having to explain to passengers about this supposedly high-end luxury car, "Well its been doing this for about the last ten years and whatever it is hasn't ever left me stranded yet." I did have my fuel pump give out on me a few years ago but that was after leaving the car parked for about nine months while the engine was out getting all new seals and gaskets (I thought I'd messed up the engine somehow when it wouldn't start but turned to to be the old pump froze up from not being run in a long time). The noise was still there immediately after replacing the pump so it wasn't the pump itself.

Check the fuel tank vent.

There's a valve under the car, near the left hand rear wheel that controls it going via the carbon canister. I've had two seize up & the tank makes some strange noises when pressurised or running as a part vacuum due to it.

You can't get the valve now days but if you open the plastic case you can take the diaphragm & spring out. Then put it back together & it looks right for any testing.