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well my civic recently developed a new anoying way to bother me. its very weird. everytime i let go of the gas, the car makes a sound identical to a blow off valve. its a subtle sound but sounds just like a BOV. only happens in drive. no neutral or reverse. btw, last time i checked, i didnt have a turbo...

 
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Wow you should be happy. But anyway, mine used to make that when I floored it right as the tranny switched gears. I know the sound. Maybe check your airbox or intake to make sure there's no loose connections. Could just be excess air escaping.

 
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it does that to me too. i like the sound personally. but like gearbox said. its your intake.

 
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It's a result of your intake. Its the sound of your throttle body slamming shut, which echos through the intake pipe.

The only ways of fixing it would be to add restriction and sound dampers to the intake tract, which I'm sure you're not up for.