Car makes noise when releasing gas pedal
March 16, 2011 9:38 AM   Subscribe

Whenever I release my gas pedal, I can hear a low pitched groan from the vehicle. The sound immediately stops immediately when I press the gas pedal again. The groan is louder if I release the gas at higher RPMs, even when I am in neutral. Any idea what this could be? The car is a 2002 Civic.
posted by ajackson to Travel & Transportation (7 answers total)
Is this in gear/moving or while in park/neutral?
posted by white_devil at 10:27 AM on March 16, 2011

When you say even in neutral do you mean it's a manual transmission? Does this mean you can sit in the driveway, rev the engine up to 4000 rpm and release you still get the noise? It's unrelated to travel speed?

If the noise happens when you are completely disengaged from the transmission then I'd be inclined to blame it on some sort of vibration. That could be a shield, motor mount, belt, pulley, whatever.

Everything else running okay? Mileage continuing to be about what you'd expect?
posted by phearlez at 12:58 PM on March 16, 2011

Does it have a turbo of some kind (common on diesel cars)? If so, it could well be that.
posted by BigCalm at 1:53 PM on March 16, 2011

I got a rumble after revving on my old Saab due to an exhaust leak.
posted by dunkadunc at 6:38 PM on March 16, 2011

Response by poster: Engine light is on. The sound occurs both while in gear, and in park. The car is an automatic but if I switch it to neutral while I am parked in the driveway the sound still happens.

It does seem related to travel speed but when I tried revving the engine when I was parked, I heard the sound. And the sound is louder if I rev it higher in neutral.

Mileage seems to be lower, I've done about 1000 km of highway driving in the past week and have noticed the decreased mileage. The sound is pretty damn loud at 120 km/h.

No turbo. But the sound sounds very very similar to a turbo hiss, but it sounds a little more grind-ey.

After everyone's answers I'm starting to think it's an exhaust leak. Is there any way I can isolate the location (if this is even the problem)?
posted by ajackson at 10:34 PM on March 16, 2011

My experience with exhaust leaks is that they're loud at load, not when you remove load. I suppose a smaller one could be drowned out by the engine noise till you release the pedal. A lack of back pressure could get you worse mileage but I think you'd have to have a leak sufficiently high that you'd have no question there's a leak.

When I had one it was no challenge at all to find - while the car was running you could feel the output from it if your hand was nearby. Something smaller could be more of a challenge but I'd still expect you to be able to feel it if you jack the car up and hold your hand nearby.

If you have someone to work the pedal you might try using the old trick with a piece of hose up to your ear. You can aim it at different places and try to narrow down the location of the noise.
posted by phearlez at 11:06 AM on March 18, 2011

Response by poster: Sourced the problem to a catalytic converter leak.
posted by ajackson at 11:57 PM on April 30, 2011

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