S80 Terrible AM reception or interference with aftermarket Nav system
 

2005 S80 with aftermaket Eclipse Nav system had high pitched whine on AM with ignition on or off. All other radio (fm, sirius) was fine.Eclipse dealer/installercould not figure it out; dealer (who had it installed before I purchased it) could not figure it out. They both thought it was because of the dual-antenna function of the factory radios or something. Another Eclipse dealer went through all and could not find issue.

A third electronics shop (speedometer and radio specialist) pulled it and sent for testing - came back all ok, but, the reinstall was much cleaner and highlighted the fact that it now worked fine with the ignition off, but the whine started immediately when ignition was turned on.

This allowed them to quickly determine that the amplified antenna in the rear window was causing the problem; system runs at 5-something volts before ignition is turned on, but the amplified antenna is at 14-something. A cheap resistor on the amplified antenna solved our woes.

I hope this helps any who are following in our footsteps.