by Neil Bauman, Ph.D.
A lady wrote,
I was interested to read your answer to the question FM Systems and Magnetic Interference. It prompted me to ask you the following:
I cannot use my Phonak MicroLink FM System in our car (Ford Fusion) because there is quite a buzz which interferes. This FM System requires that my hearing aid (ReSound Pixel PL80 DVI) be set on one of the T-coil settings (T-coil alone, or both T-coil and Microphone).
The only thing I suspect is that the car is outfitted with ‘Microsoft Sync’, which allows you to connect an iPod or other device to play through the car’s stereo speakers. The buzz occurs when the sound system is not even on.
I can’t think of any other reason, and have queried Ford, but they never responded.
The reason for the buzz in your car is that your car is producing the racket—probably the ignition system. If the buzz gets louder/faster when you step on the gas, you know it is your ignition system. It can also be produced by the various electric motors in your car—fans for example.
Some cars are very magnetically noisy (the buzz you hear via your t-coils) and others are very quiet. In future you might want to turn your t-coils on when you test drive any new car and buy based on how quiet it is (among other things).
The good news is that a good automobile radio technician can put suppressors in various places in your car’s electrical system that will suppress most of this racket. We HAMs (radio amateurs) used to do this all the time in our cars so the alternator hash wouldn’t get transmitted, so I know it works.
Your MicroLink is not a fault. It’s the t-coils in your hearing aids that are picking up the buzzing from the car’s electrical system. That’s why you hear the buzzing whenever your car is running and you have your hearing aids in t-coil mode whether the FM system is on or not.