Octavia 2016 Bolero - Hiss after adding aftermarket amp/speakers

Hi, i just finished adding amps/speakers/subwoofers to my Octavia.
And the sound quality and volume are greatly improved.
However there is an anoying hissing sound as soon as i turn on the radio, its there whether the engine is running or not.

My powercables are run on the left side of the car, signal wires on the right.
Ground is solid. Measured 0.1 ohms from the battery negative to my ground on the amp.
Today i bought some Stinger 8000 RCAs and a SinusLive ground loop isolator.
I ran the RCAs straight through the cabin to the amp to avoid any interference.
I tried the ground loop isolator at either end of the RCAs.
Neither of them changes anything.

Then i found an old rusty JVC radio from a 1000 years ago, and installed that with all the same wires, and there was no hissing at all.

Is the stock Bolero HU just bad?

Is there another aftermarket headunit i can install to retain all the features of the stock radio? (Tyre pressure, car status, park assist and so on)