Kika

high pitched whine is a common problem particularly with amplified stereo systems. it happens due to poor grounding of the stereo and it's components. The alternator essentially adds an AC component on top of the DC voltage, that an amplifier will amplify. A large capacitor will filter out that AC signal and eliminates, or diminishes the signal below threshold.

loose connections, unplugged wires and small resistances between "grounds" can all cause problems.

Cars are notoriously awful audio environments.

PRSWILL

I have a similar unit and it works great. Grounds on these cars are so so at best

Kika

FIFY