996T - Intermittent hum from front end

[996TT02]

Got out of car to take some pics, and as I generally do, I let it idle.

It was then that I noted a humming noise from the front, I did not investigate fully but it was audible on the drivers side, in the front wheel area.

The sound is a hum like thing but I noticed it because it was intermittent, i.e. it had a frequency that was similar to a ringing tone... what you hear when you are on the phone calling someone waiting for them to pick up... hummmmmmmmmm, (pause...) hummmmmmmmm, (pause...) etc etc.

Is this normal and something that I never happened to have noticed before?

Since I then got quite sensitive to this sound I think I also heard it while actually in the car and driving and convinced myself that I could also feel it through the wheel.

Any ideas? Only just got back from holiday drive so have not looked into it at all, perhaps the PH knowledgebase will give me a shortcut!

[blueg33]

I am not familiar with 996tt, but other rear engine cars tend to have a low pressure fuel lifter pump at the front, it could be that if there is one.

[Crimp a Length!]

Fuel pump without a doubt. Not a problem, my first one used to do it.

[996TT02]

Crimp a Length! said:

Fuel pump without a doubt. Not a problem, my first one used to do it.

Thanks that's good to know, on both counts...

It's a noisy car overall so I could very easily have overlooked this sound previously.

[Pope]

Its the tank vent valve pulsing.

Sounds much like the sound of a distant oil tanker on a foggy day....

If you remove the fuel cap it will stop; it's perfectly normal. It's not the in tank pump as that would be a constant sound not intermittent.

[blueg33]

Pope said:

It's not the in tank pump as that would be a constant sound not intermittent.

Unless its broken or had a dodgy connection.

[996TT02]

That's great, I will also try the cap removal test...

[Homer J]

Mines has done this intermitantly since I bought the car over 4 years ago. I've just learned to live with it.

Mine does it about 30 secs after start up, noise lasts maybe 5-10 secs. After that it's completely random. It can do it a few days on the trot, then go a few months in silence.....Always at tickover though.

I've noticed on mine it doesn't matter if the tank is full or nearly empty.

So is a new vent valve required to shut it up?