I've driven my "new" 2005 GT about 60 miles total so far. Something just happened and I'm a bit perturbed. Now, every time I press the gas, I hear a "tone" kind of sound from the back. It stops right after I let off the gas. It isn't related to RPM, but rather if I'm putting power in via the gas pedal. I press down to accelerate, I get a tone. I let off the gas, tone stops right after. It doesn't get louder or softer with speed, or how much acceleration, nor does it sound if I'm just revving in neutral.

I don't think it's the vacuum pump, but I fear it's the vacuum pump running. does this make any sense? I can't imagine what it could be that would be tied into the gas pedal like this. I haven't pulled codes yet, but I was hoping this is something minor that everyone knows about?

 

Have you checked your speed warning alarm settings? I ask because you mention "tone" sounding. However, if it is the speed sensor, I believe you will get an alert on the dash. It might also be the sound of your secondary fuel pump coming on (if it is faulty).

 

Perhaps an audio recording from your cell phone would be helpful. There are instances where the vacuum leak is evident with light acceleration. When the big vacuum (13mm) line at the rear of the engine intake manifold has a slight crack in it behind the steering rack ( left side US).

However, a smoke test would quickly reveal this theory. Furthermore you did state the tone disseminated from the rear. The other pump in the rear is for air suspension. The thought of this pump running in tandem with acceleration doesn't seem plausible.

Regrettably 2005 models were subject to the infamous vacuum leaks. A healthy pump running sounds like it's breathing a bit. Like I said sometimes under light acceleration it'll run and then stop when taking your foot off the accelerator. I'm still not sure if this is the case more information needed.

 

Interesting you brought that up. Maybe that solves it. I was dorking around with the suspension settings and I moved it from the midpoint to "full comfort" or whatever the opposite of "sport" is. I wonder if this started up right after I made that setting change. I'll try putting it back to midpoint and see if it goes away. thanks yet (again!) for your willingness to help out.

Supposedly, the car had all the vacuum hoses replaced when there was a transmission repair, which is one of the main reasons I bought this car.

But, it does seem to suffer from every single malady common to the 2005, there was a sagging headliner (fixed) an inop third brake light (soon to be fixed), the TPMS is completely inop/missing/unplugged and if you've seen my other thread, the stereo is absolute garbage. But the engine idles great, it came with a flawless interior and exterior (how, I don't know, my wife's SUV looks like it's been through a war zone and it only has 25,000 miles and two years of age) and the suspension/steering alignment/everything seems to be absolutely fine.

But I know something is weird, that sound when I press the gas pedal sure sounds like a pump or a leak, and it seems computer-controlled, since it goes on almost immediately after pressing the pedal and goes off almost immediately after releasing. Not exactly coincident, so it seems like it's being controlled.

I just asked my wife if the sound came before or after I made the suspension changes, she says "before", but isn't sure.

I'll see if I can get a recording of it, but it's not all that loud, but loud enough in the quiet interior to drive me batty.

 

Sometimes the 13 mm vacuum lines that run to the back of the intake manifold are not replaced with metal. Thus, when performing a tune-up they're hard to disconnect and get a small crack behind the steering rack while being manipulated. Pull the little plastic valve cover piece off the back of the intake manifold and see if there are two black plastic lines running to the manifold. You could always take a picture and upload it, as well.

Pump the brakes while engine is running at idle in park. How many pumps does it take before you hear the vacuum assist pump activate. The vacuum pump is located left front wheel well. Leave the driver's door open so you can hear it. Also this will help identify if that is the culprit while you're driving.

 

took everyone's advice. Pressed the brake pedal a bunch of time with the door open and the window open, couldn't even hear the pump go on. Ran fault codes, got only "exhaust flapper valve" which sounds unrelated and unimportant.

Sound is still going. I recorded with my phone, it is super hard to hear, but it is there.

If you turn the volume up and listen, it is what sounds like a faint train whistle on acceleration.

Here is the sound.

 

Not able to decipher the specific sound. There is the normal road noise and background engine sound. Then there is a knocking sound. At the very end heard a slight sound that resembled air being released.

The good news if pumping the brakes doesn't immediately make the vacuum pump run, fantastic.

 

I have a 2005. Heard the same sound. It was tha vacuum pump. On left hand drive it’s located in the drivers side front wheel well. Mine was running all the time with any level of acceleration.
turns out the problem was cracked vacuum lines. They are plastic and deteriorate with age and possibly heat.
unfirtunately they run over the transmission and cannot be replaced without removing the engine.
I had it done at an independent for USD $7,000. Replaced the lines with steel ones.
hope your sound is from something different.

 

your problem is the exhaust flapper valve. it opens with the gas pedal the flaps are inside each muffler and are vacuum operated.

some ppl put a golf tee in the vac line so muffler sounds louder as flaps will be open all the time.

 

That: 1) makes sense 2) is awesome

Thank you! I am certain you're right, it does not sound like a vacuum line at all, and the ODB shows that as an error.