1. Use the earphone to connect with the car MP3 and car navigation AUX (3.5mm interface). If the sound heard from the earphone is no noise at this time, it can be confirmed that the noise of the car device is caused by the common ground.2. Use the audio cable to connect the battery-powered mobile phone, or MP3 (note that the mobile phone, MP3 is not connected to any power source on the car, such as a telephone), and the AUX of the car center console, and play the music of the mobile phone. Noise can confirm that the noise caused by the common ground.3. Computer, amplifier, stereo, CD: Use a passive headset to plug in the computer to hear if there is noise, use the phone to plug in the amplifier, audio audition, if there is no noise, the basic judgment is caused by the common ground.4. After starting the car, the installed amplifier has a current sound. In some models, the throttle is larger and the current is louder. This product can solve this problem.5. There is a current sound between the amplifier and the speaker or the sound. This product can be installed between the amplifier and the speaker.When the laptop is connected to the projector and the amplifier is connected with noise, you can connect the adapter to the power supply or use the battery. At this time, unplug the amplifier and , or unplug the projector and the noise will . Then you can use the headphone and amplifier of the computer. Add a common ground isolator to eliminate noise.Material:Composite materialSize:5 x 3cmPackage Contents:1 x Audio Isolator