Not sure about the second gen cars, but there is an axillary antenna connection to the rear window defogger wires. If this gets disconnected it can cause some weird problems on the first gen cars.
Gen1 cars (refresh only with the diversity antennas((glass and roof))) also had a signal booster...powered by power that was backfed up the antenna lead..I cannot recall, but I think on the gen1 cars, it was one unit...any chance you checked the unit for power?Seems to be a common issue for folks when going to an aftermarket radio done by a nonpro Shop...
Not sure how the key issue might be combined....different frequency...99% sure it has a separate receiver....
Know every spring when the trees get leaves, many of my favorite stations from Boston drop in signal strength here in NH...about 40 miles from the stations....the marginal ones get more static...a could become annoyingly so till I am 5 miles or so closer to Boston...any chance you might be chasing a ghost caused by the seasons changing or is it VERY SEVERE even on local stations?
INPA shows full signal strength on my test local channel, and selecting antenna diagnostic and going through all the antenna's yields no change, all of the antenna's had similar static
Check the ground connection on the back of the head unit. Mine was not connected properly from the factory and was finally corrected by the dealer some 6 months after delivery.
