W-4000 Power Conditioner Power Purifier Audio Noise Power Filter with EU outlet | eBay
Amazon.com: Acouto Car Audio Noise Filter 12V Power Noise Suppressor Filter Car Stereo Audio Filter Noise Isolation Reducer High Performance for Amplifier Speaker Car Audio Systems : Electronics
Low-cost audio filter suppresses noise and hum - EDN
Basics of audio filters
Audio Isolation Stereo Filter, Noise Suppressor Wearable Audio Noise Filter, for Car Audio : Amazon.in: Electronics
Noise Filter Circuit: Improving the Sound on your Listening Device
automotive - DIY car audio noise when the source device is charging from the same power source - Electrical Engineering Stack Exchange