Cars

What’s causing a thumping sound when I hit the brakes?

John Paul, AAA Northeast's Car Doctor, answers a question from a reader hearing an unsettling noise when braking.

The 2018 Acura RDX. Acura

Q. I have a 2018 Acura RDX with 29,000 miles. I’m hearing a thumping sound from the right front when applying the brakes. I checked the tire and there is no visible damage. The brake rotor also looks okay. I still have a warranty since it was a certified pre-owned vehicle. What could be wrong? 

A. A thumping sound is typically a loose component or an out-of-round brake rotor. The issue could be a loose caliper mount, a pad moving, or even a suspension part. At this point the only thing to do is take the car back to the dealer to demonstrate the problem and get it fixed. Additionally, Acura did issue a revised brake rotor part for this vehicle due to noise concerns. 

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Q. I have a 2007 Nissan Sentra. I’ve replaced the compressor and recharged the A/C system correctly. Now, when the weather or vehicle is hot inside, the air conditioner will not work. The compressor just cycles on and off.  Otherwise, the AC blows cold at about 40 degrees. What could be the cause?  Could it be an AC pressure transducer sensor?

A. On an 85-degree day, I would expect the duct temperature to be 55-60 degrees. Typically, rapid compressor cycling is due to a low refrigerant charge. You didn’t say what the pressures are, but I would expect to see 200-220 on the high side and 35-45 on the low side. If the pressure is normal but the switch is reading a low pressure, then it will cycle the compressor. The switch sends a signal to the ECM (computer), so you would also want to check proper voltage just to make sure there isn’t a wiring harness issue. 

Q. I have a 2021 Honda Pilot with just 7,500 miles. I’m getting a crackling sound periodically coming from the AC/heat vents. The dealer says it’s a loose connection that requires removing the dashboard to replace. Is it worth going through this process and risking future problems with the dashboard or should I just live with it?

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A. It is a very time-consuming job to completely remove the instrument panel — almost a full day’s work. Since there are no known issues with this that I am aware of (no tech bulletins), my concern would be that after taking it apart and putting it back together it could be worse. I suggest just having the dealer note the issue, so that if it gets worse, it will be easier to identify. Then have it repaired. 

Q. I have some issues with my 2009 Lexus RX 350 that I bought certified used in 2014. I use the preset buttons when getting in and out of the car to adjust the seat height. For the last three years, the seat has been making an awful groaning sound when I change the positions. This only happens when it is warm or hot outside. During the winter there is no noise at all. Also, the driver’s window slows down when it is warm outside and sometimes makes a gritty sound. The passenger mirror doesn’t stay in the position where I previously left it. Finally, the radio sometimes shuts off when I hit a bump.

A. From your description it sounds like four separate issues: The power window motor and seat motors (there are three at about $500 each) may be getting near the end of their useful life. The mirror could be worn, or have a faulty controller or motor. The radio could be a poor connection to the radio or internally in the display screen. At 13 years old, it is not unusual to see some electrical issues. It is also possible that there is some sort of rust/corrosion issue bridging some of the problems. It would be best to start with a basic check of the electrical system.

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John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your car question to [email protected] Listen to the Car Doctor podcast at johnfpaul.podbean.com.

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