Satellite radio install probs

[Auf los!]

I installed a Sirius/XM Onyx Plus in my 2001 today. Managed to mount the antenna under the cowl on top of a plastic box, found the large grommet behind the battery to run the cable into the interior. Found and used the phone connector wires so the receiver has switched power. Modified an old GPS suction cup mount to stick the receiver to the windshield. Bought an aux cable off of Amazon, and found the "secret" instructions on this forum to access the AUX function in my CDR220, thanks so much!

It works and I'm getting music, but there are two problems. The first is that I am getting some nasty buzzing, kind of like ignition noise, that I can hear between when I turn the ignition off and the receiver dies. I am suspicious of a cast metal box mounted to the top of the tunnel and inside the console where the phone connector was. The 12v cigarette lighter plug that came with the radio is intact...I connected a 12v socket to the phone connector, and the plug and socket are resting inside the console, basically on top of this metal box. What is that box? Could that be the source of the interference? If I put some distance between the socket/plug and the box will the buzzing go away? Any other ideas for getting rid of it?

The other problem is that about an hour after I buttoned-up the car and put the alarm on, the alarm went off, I think for the first time in the ten years I've owned the car! I disarmed the alarm and it went off, but if I screwed something up, why would it wait an hour for it to go off? How do I fix that?