Piston Slap: An Accented Whooshing Sound?
I have a 2007 Hyundai Accent 5-speed manual hatch. When I’m driving, sometimes I’ll hear a little ‘psssht’ noise as I pass through 2500 rpm. It almost sounds like a tiny blowoff valve under the car.
My thinking is a small leak in the flex coupling on the exhaust, though it seems odd that it would only happen at a specific rpm.
Sajeev writes:
ZOMG SON Y U NO BRAG ON UR TURBO!?!?!?
But seriously, I have no idea why that’s happening. First I was thinking about that exhaust leak, but (like you said) that wouldn’t be RPM specific. Or perhaps an intake tube leak, but one significant enough to make that much noise wreaks havoc on a computer’s ability to control the air/fuel ratio. Maybe an EGR thing, perhaps a vacuum line gone bad? But the odds of that being “bad” enough to make that sound? Not likely.
Did you install an aftermarket intake tube assembly? Or even just a K&N filter? Try returning it to stock and see if that does anything.
If that’s not the case let’s go with the exhaust leak. Go to an exhaust shop and put the Accent up in the air: perhaps they will see or hear something that will explain the problem. What say you, Best and Brightest?
Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
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Does the noise occur if you rev the engine in neutral while standing still? If so, get someone to rev the engine while you go listen under the hood with a 3 foot piece of rubber hose to act as a stethoscope and localize the noise. Jack the car up (on jackstands or a hoist) and crawl underneath if necessary. My guess is something vibrating since it is rpm related. Exhaust leaks are more throttle opening related in my experience.
Had a very similar RPM-specific [around 2400] noise from an 03 Focus; Turned out to be the flex pipe, identified only after warranty had expired of course.
It's the VTEC, yo! (JK)
Nine months later, and the car more or less quit doing it. Still happens every once in a while on cool rainy days. Go figure.