Ground loop... i.e. different grounds b/w source (sat radio) and head unit is causing the "ignition" noise. Install ground loop isolator (from amazon or radio shack if any still around) and noise will be gone.
Alarm - you might have dislocated the radio frame alarm ground when installing the AUX in to radio. Pull head unit again and make sure firmly attached (upper back left corner as I recall).
Good luck
