FAQ: Getting Rid of that Whine or Buzzing Noise in Your Speakers
So, now you've installed your PC and hooked it up to your stereo. It rocks! Except for the fact that there's this "buzzing" noise, or "whine" coming through your speakers! It may seem to pick up when you accelerate and slow down when your rpms go down, or it may just be a persistent buzzing noise. Either way, it's ruining your install! What's up and how do you get rid of it?!
The noise is nearly always caused by improper grounding of your system. According to the wikipedia, a ground loop is caused by an unwanted current that flows between a conductor at two points that have nominally the same potential.
Wha?! Here's what's happening. The chassis of your car serves as a ground. Often when installing PC's and amplifiers, they are located in different parts of the car. The ground wire for both units is often grounded in different spots on the car. While the metal chassis is a decent conductor, it isn't perfect and there can be a difference in electrical potential between the two grounding points. The result is a buzzing noise, or a whine, often coming from the alternator, which accounts for the change in the sound as the alternator spins faster and slower with engine rpms.
There are two possible solutions:
1. Ground all components to the same point. This will reduce the potential and should greatly reduce any noise.
2. If number 1 is not possible (and it often is not), use a "ground loop isolator", available at nearly all electronics stores, or car audio suppliers. This device prevents a direct electrical connection between the two sources and will usually fix the ground loop.
The source of the whine can be mysterious and very difficult to track down even if you perform 1 & 2, above.
For more information, search on terms: "Ground loop", "alternator whine", or "buzzing".
Car audio professionals/geniuses, please post any tips or tricks in this thread. Thanks!