Ground Loops: Car Audio Hums and Whines

How to get rid of annoying sounds

boy covering his ears
If a whining noise from your car stereo has you covering your ears, a ground loop may be to blame. Daniel Grizelj / Stone / Getty

Question: How do I get rid of the whining noise when I use my aux input?

My head unit works just fine when I’m listening to radios or CDs, but I’ve been having a problem ever since I started making use of the auxiliary input. I have one of those satellite radio tuners that you can plug into an aux. in, and whenever I try to listen to it I get a background whine sound that seems tied to my engine RPM. I tried plugging in my iPod, and I get the same thing! Is there any way I can get rid of this obnoxious sound?

Answer:

It’s impossible to say for sure without looking at your specific car audio setup, but it sounds like you’re suffering from a classic ground loop problem. Ground loops occur whenever two components are grounded in different locations that have different ground potentials. That can create an unwanted current, which introduces the sort of interference that you’re hearing (which is often described as a hum or a whine).

The right way to fix a car audio ground loop problem is to make sure that everything is grounded in the same place. While you don't technically need to ground everything in the same place, it is important that every ground you use has the same potential. In the event that you can't, or don't want, to fix the problem the right way, the easy way to fix a ground loop problem is to use an in-line noise filter.

Car Audio Ground Loops

Although there are a lot of things that can introduce unwanted noise into a car audio system, ground loops are the single biggest culprit.

This noise problem can occur any time that two audio components in the same system are grounded in different locations. If those two locations have different ground potentials, an unwanted current flow can be introduced into the system, which can create noise. If the difference in ground potentials is removed, the unwanted current flow ceases, and the noise goes away.

In home audio systems, ground loops usually happen when two components are plugged into different outlets, and fixing the problem may be a simple matter of changing where you have things plugged in. Unfortunately, the matter of grounding is a little more complicated in car audio systems. The chassis — and any metal that’s in contact with it — is the ground, but not all grounds are created equally. For instance, grounding one audio component to the chassis and one to the cigarette lighter is a classic situation that can lead to the creation of a ground loop — grounding a head unit to a cigarette lighter instead of the chassis is one major way that ground loops are introduced.

If you’re suffering from a ground loop, the right way to fix the problem is to tear down your sound system and attach the grounds from components like your head unit and amp directly to the chassis in the same place. That’s why it’s so important to make sure that everything is carefully plotted out during the planning stage of any new car audio system, and then hooked up right during installation. This is definitely a situation where an ounce of prevention is worth a pound of cure.

Isolating Ground Loops

While the right way to fix a ground loop is to deal head on with the differential in ground potentials between different components, it’s definitely not the only way.

If the thought of tearing down your audio system, locating the grounds, and then putting everything back together doesn’t sound appealing, then you might want to look into an isolator.

Ground loop isolators basically consist of an input, an output, and a transformer. The audio signal enters the isolator through the input jack, passes through the transformer, and exits through the output plug. Since there is no direct electrical connection between the input and output, the ground loop (and any interference it generates) is effectively “isolated” from the signal.

While these noise filters are technically just band-aids, and your underlying problem will still exist, they’re band-aids that generally work pretty good.