What’s that mysterious rattling sound in my car’s transmission?

John Paul, AAA Northeast's Car Doctor, answers a question from a reader whose Lincoln MKZ makes a strange sound at a certain speed.

2017 Lincoln MKZ
The 2017 Lincoln MKZ. –Lincoln

Q. I own a 2009 Lincoln MKZ. It’s a very nice vehicle with only 70,000 miles on it, but it does have one issue. When driving at 20 to 25 miles per hour, the transmission makes a rattling noise. Once it is over or under those speeds, everything is fine. The car has new tires, new brakes, and it’s very well cared for. Any ideas?

A. If all of the usual sources of noise, such as mounts and exhaust shields, have been checked, then the only way to find the source is to take apart the transmission. This would be an expensive proposition. Before I undertook this, I would have the car road-tested with a transmission specialist who has seen this before. One possibility is that the car is missing a support bracket for the intake manifold. When this bracket is missing, you’ll get a low-speed vibration. As the car has aged, this vibration could be causing the exhaust heat shields to rattle and make it sound like the noise is coming from the transmission.

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. Email your car question to jpaul@aaanortheast.com.