Check to see how close the RCA's are to the power wire.

What kind of RCA's did you use? High quality nicely shielded ones or really cheap ones?

Check ground, and double check the ground.

What size power cable did you use and was it high quality and or well shielded..

Are there other power wires where you ran the RCA's?

Did you try maybe running the RCA's down the passenger side and the power down the driver side?

Check the Radio's Ground.

You can also at the battery use wire wrapped magnets in line of the power connector to see fi that helps with noise. I have seen it done on other cars.

try an RCA noise supressor as a last resort...

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon