I'm having a tough time figuring out the source of radio noise in my 1997 S500. With the key in the number 1, or accessory position, the radio, C/D and cassette all work perfectly, but when the key is in the number 2, or run position, I have very bad noise with the radio bands even though the C/D and cassette still work perfectly. This happens whether the engine is running or not.

I have 2 factory radios and a new after market radio. All 3 have the same symptoms.

I also installed a new Hirschmann universal antenna but it made no difference.

I was wandering around on ebay looking at used amps but found a part called an "antenna amplifier noise supressor" listed and wondered if that could be the problem. Here's the listing: Mercedes W140 S320 98 99 Antenna Amplifier Noise Suppressor 1408202189 21048 | eBay

Does anyone know where this part is located in the car?

Thanks, Bob Short

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire