01 porsche carrera 4 engine noise

Hello. Im doing A Kenwood 9960 ddin nav unit in this car w/ an arc audio 5080 5ch amp. My issue is when i put the radio in the dash , its picking up engine noise. outside the dash there is no problem. I have tried different RCAs, ground loop isolators, different ground and power points to no avail. I even tried different materials around the radio to try and shield it from the noise. im running out of ideas on what to try and was wondering if anyone could suggest something. thanks in advance.

Forgot to mention, when i put a ground to the rca ground the noise gets worse. with or without the GLIs. i can literally hold the HU and the cables up above the dash and everything is crystal clear.

Should use a Chevy.

Try disconnecting the rca from the deck and leave them in dash, and put deck into "clean" area and turn on.  If its quiet, try a differet deck in dash.  If not reroute rcas.  Noise on from radio and cd?

Does that car have flouecenent back lighting on the gauges?