What type are your two players? (2, 2a, etc.). Which one is OK, and which isn't? Which is the newer one? What versions of software are you running?

If you get noise, you may have a car that has a lighting indication wire carrying a PWM signal to modulate lighting level, rather than indicate lights on/lights off. There is no standard for this: if this wire is incorrectly connected to an audio lead, or for some reason used as an earth line, it could be injecting noise into the ground line of the system. One release version of the software was modified to deal with PWM input on the lighting sense line. Check your harness wiring to the sled.