Hiss from Archos 504 into car radio aux input

[turf]

I use a 504 to play music through the aux input of a car stereo. Sometimes, there is a good deal of hiss such that I have to turn down the aux input gain on the stereo to minimum (-8dB). Other times it is fine at a gain of 0dB or even +4dB. It is not the music since I have heard this, or not, on the same tracks. I have tried three different aux cables and the intermittent problem has occurred on them all so it is not the cable. It could be a coincidence but it appears to be worse when the battery of the 504 is less than half charged. I have never heard this hiss when using the 504 with headphones.

Could it be the player building up a charge (although it does not lessen the problem to touch the unit)? Are there any other reasons it would do this?

turf