I replaced the factory cassette with an Alpine CD player on my non-Boze '96 SE. Everything is quiet and sounds great except for the low end of the AM radio band. I used a Sosche diversity antenna adapter and the noise is present no matter which antenna is connected. It's not alternator whine or ground loops and it's only present when the ignition key is on. The noise gets worse when the antenna mast is near the keyless remote box wiring harness and goes away when I unplug the antenna.

Anyone have a clue how to get rid of the noise?
Thanks for any help.

 

Answering my own query for any lucky sole searching for a similar problem -

I took the whole thing apart and after grounding the shield and a few other things that didn't matter, I learned that the diversity antenna adapter was plugged in backwards. The adapter will only select one of the two antennas, you just don't know which one (the tabs lined up and I thought the 'default' connection would be the mast). So it was using the antenna built into the back window instead of the mast, and reception of vertically polarized AM suffered. Also adding to what I thought was ignition noise looks like it is interference caused by the remote keyless receiver, which is mounted next to the antenna motor. I think the diversity system from the stock radio helped cancel that noise, and the problem magnified when it was only using the window antenna instead of the mast. Much better now.