Car Makes Noise When Accelerating

Reader Question

My son drives a 2001 Hyundai Sonata. Intermittently for the past six weeks, when slowing down to a stop, the car makes a loud, clunking sound. When accelerating from a stop, the car makes a loud, clunking sound, there is no power, and the engine light comes on, but the revs are up.

We took it to a transmission specialist who diagnosed that the knock sensor needed replacing.

He replaced the sensor and changed the transmission fluid (which did need changing). The problem disappeared for 9 days and then re-appeared. My son was accelerating on a green light after stopping at a red light, and had to pull to the side of the road because there was no power.

The car behind him almost collided with him. We took the car back to the transmission specialist today to run some more diagnostics, but I am afraid this is going to cost us a fortune before the real problem is diagnosed and fixed. Please help. Thank you. Jennifer

Hello Jenny

I do agree with the first diagnosis of a bad vehicle speed sensor, and it is strange the vehicle was fine for 9 days after it was replaced.

I don’t know if I would think the sensor was the cause of the noise though, for that I would look at the engine and transmission mounts and see if one was broken. If the engine or transmission is banging about it could have damaged the sensor…and the new one.

You might ask them if they checked the mounts, especially if they say the new sensor is bad…..something had to cause the new failure. It COULD be possible that there is an internal problem in the transmission…..but try to rule out the more obvious items first.

Let me know what you find out.

Please share this with your friends,
Austin C. Davis

4 Comments on "Car Makes Noise When Accelerating"

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  1. Andy T. says:

    I had a similar problem noise in my car too. Mechanic found a small exhaust leak at the manifold under the hood. When I would accelerate real hard it would make this hissing noise, drove me nuts.

  2. tj says:

    I have a 2006 hyundai sonata and just today it don’t want to start rite away and when I did get it started when I got on the road it loses power when I hit the gas the engine is not dieing either I kinda need an idea of what I’m looking at ty

    • Austin says:

      This could be something as simple as needing a tune up. I would start by checking the spark plug wires for replacement, if you have more than 60,000 miles, I would probably just replace them and the spark plugs as maintenance regardless. If you don;t have the normal spark plug wires, but have the new ignition coils, then I would not just replace them without testing them first. They are not usually just replaced unless there is a problem.

      Lack of fuel pressure could also be an issue. A restriction in the fuel filter, or a weak or bad fuel pump should be tested. If you have a normal external fuel filter, I would also just replace it as maintenance. Some models dont have a replaceable filter.

      Having a mechanic test the fuel pressure at the engine with a fuel pressure gauge would be the next thing I would test, although fuel pump replacements are not common to me on this vehicle.

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