Once in a while, when i start the car i hear a pumping sound coming from the rear of the car. If i leave it, the sound remains, however if i turn the car off and back on, the sound vanishes..

Because it comes from the rear, i want to think it is something to do with the fuel, but i really have no clue. It doesnt happen alot but when it does, i hate turning the car off and back on. It always tends to happen when alot of people are around...not when i am alone in my garage..

Anyone have any ideas?

 

Like a quick pumping woosh? You should get that for a few seconds if you turn your car on (not over), and all the fuel needed to crank should be ready.

But if it's constant while you're driving around, perhaps either your pump itself is failing, or maybe the line is pinched somewhere? Intermittent problems really are the worst.

 

Its like a constant pulsing whine and it does not go away. Like i said, it only happens once in a while and all i have to do to stop it is restart the car. I was just at the dealer and they have no clue what it is because anytime i go their it wont do it, so i have to explain it...

 

Could it be the fuel sloshing around in the tank? Does it continue when you drive if you dont turn the car on and off?

 

It happens when i go to start the car in the morning as well as other times. It sounds like a pump. Next time it happens i am going to record it and post it, it really makes you no sence.

 

Maybe its the ABS pump? I did have a mysterious humming rattle from time to time in my old car, but never got bad enough to check it out. I'd try to find which conditions (weather, temperature, time sitting) set it off, maybe then the dealer can find it.

 

Probably the elelctric fuel pump in the tank. FI cars need high pressure to work so pump comes on when first keyed up in AM or after sitting long enough for system to bleed down to get ready for start. Some hear it and some not. In enclosed garage you're likely to hear it, in open air location probably not. Sounds like everything just doing its job.

 

I know it has something to do with the fuel pump, however it came on today after i was in the grocery store for no more than 20 mins. I gave it a chance to go away but after 30 mins, it was still their. I didnt have anything to record the sound and the mazda dealer was closed by this time...
But i do think it has something to do with the fuel tank because it is coming from the rear, passenger side of the car and can clearly be heard from inside the car and outside the car. It also stays constant and doesnt fade.