Q: My Kia Forte is making a grinding knocking noise when I put it in drive and accelerate and at about 5 mph and up it goes away unti

asked by on

I got a diagnostic done and it said it was the manifold but the sound is comin from the side where the drive belt is

My car has 75000 miles.
My car has an automatic transmission.

Hello. Exhaust systems can make a variety of sounds that we would not intuitively expect. When I was first learning about exhaust systems I was surprised to find out how dynamic they can be. I am assuming you are speaking of the exhaust manifold since the intake manifold doesn’t usually make a noise that sounds like a knocking, but the exhaust frequently can.

When your car is not in drive, the exhaust pressure is much less than when it is in gear. Putting your car in gear adds a load to the motor that can be felt in the exhaust system. Once you begin to move, the flow increases and the exhaust can suck in air instead of pushing it out. This is known as the venturi effect, just like how a carburetor pulls fuel into a motor. Of course, newer cars don’t use carburetors anymore. When you hear the noise, the exhaust is pushing out air. When the sound goes away, exhaust air flow increases enough to create the venturi effect.

Another phenomenon that occurs in exhaust systems is they can leak when they are cold, expand and seal themselves once they warm up. This could be another part of what you are experiencing. As for where the sound is coming from, sounds can be tricky to locate. A big part of car design and engineering is managing all the resonances that transfer through your car. Engine mounts, shocks and struts, brakes and many more components are all part of systems in place to manage noises and vibration. If you hear the sound from inside the car, it is very difficult to be sure where exactly the source of the sound is. I have spent quite a bit of time chasing sounds on one end of a car only to figure out the source is at the other.

If you would like a second opinion, a professional from YourMechanic can inspect the noise for you so that you can have this corrected properly.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. My Kia Forte is making a grinding knocking noise when I put it in drive and accelerate and at about 5 mph and up it goes away unti

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Car hard to turn after starting

If your car's steering wheel is difficult to turn, and making noise when you do so, it is possible that your power steering fluid has run low or perhaps leaked out. I would recommend having a professional technician, such as...

Q: How do I change the settings?

Your truck allows you to customize some options to better suit your needs as a driver. The Settings section of the message center is where you can change these options. To change the Settings of your Ford F-150. Use...

Q: Problem with battery light

Hi there. If you went to the auto parts store and they completed a scan and indicated a starter problem, then it is quite likely that the starter is NOT the problem. The procedure these companies use to diagnose a...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...