I will be near my 990 in about two weeks and will try to duplicate your effort with one of the many radio stations I don't get. You say you noticed this right off the bat when you got your 990? I listen to analog all the time via radio and phone and never experienced an issue but my hearing isn't the best. With the white noise what should I hear if the problem exists? Some sort of frequency mod that changes when I change the sample rate? What setup do you have for the following statement:

I have the analog inputs connected so that this signal can be routed to Zone 2,

Is it possible that the input wiring is causing the add signal to be generated and summed with the delay through the digital path? I am only guessing but there is probably a way to crosstie the digital signal to the analog buss with some creative wiring in the back. Could it be some sort of crosstalk problem?