There could be a combination of things to try. Rasmataz is right about the ground problem. First of all, there is no ground wire in the original radio wiring harness. Chrysler used a separate ground wire or braided strap that bolted to the back of the original radio. If the installer didn't run a new ground wire, the radio could get grounded through the shield of the antenna cable. This is a very poor, unreliable ground and can cause a variety of problems.
To add to the misery, your car uses "pulse-width dimming" for the dash lights. That means that instead of using a very reliable five dollar rheostat to adjust the light brightness, your car uses an expensive computer module to turn the dash lights on and off hundreds of times per second. The ratio of on to off time determines the average bulb brightness. This pulsing voltage can enter the radio through one or both of the two power wires, or it can be radiated into the antenna. Chrysler original radios have filter circuitry to prevent this kind of interference. Most aftermarket radios of any quality have similar circuitry, but it's not always as effective at eliminating the noise. If you do not hear the noise when playing a cd, the hiss is coming in through the antenna.
The first thing to do is to pull the radio out and check the splices between the car's wiring and the Kenwood connector. An amateur would have twisted the wires together and taped them. That's a sure recipe for disaster. A lazy installer uses crimp-type butt connectors. Professionals slide the strands of the wires together, then solders them and covers them with heat-shrink tubing.
If the splices look ok, check for a proper ground wire, or use an ohm meter to measure resistance from the radio's metal case to the car body. Re-measure the resistance after unplugging the antenna. If either reading is more than a few ohms, run a new ground wire from the radio case to the car body. If that doesn't stop the hiss, you might consider going back to an original radio. It's hard to beat the quality of the Chrysler cd / cassette combo radios.
Monday, March 23rd, 2009 AT 2:40 AM