Stereo Audio Isolator Common Ground Anti Interference Noise Filter Current Sound Eliminator Item Type: Common Ground Isolator Material: ABS Size: Approx. 45x30mm/17.7x11.8in Determine if the noise is caused by common ground: 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 supply on the car, such as a telephone), to the AUX of the car's center console, and play the music of the mobile phone. If there is no noise, it can be confirmed that the previous noise is caused by common ground. 3. Computer, amplifier, audio, CD: Use a passive headset to plug in the computer to listen whether there is noise. Insert the headset in the amplifier and the audio, if there is no noise, the noise 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 the problem. 5. If there is a current sound between the amplifier and the speaker or the audio. This product can be installed between the amplifier and the speaker. 6. When the laptop is connected to the projector and the amplifier at the same time, there may be some noise. At this time, unplug the amplifier or the projector and the noise disappears. Then you can use the product between the headphone jack and amplifier to eliminate noise.