I experience a bunch of problems with my 2007 Mazda 3's electrical system:
The most annoying issue is that I hear [a rather loud] engine noise when I connect a phone to the AUX (3.5mm audio jack) line while it is simultaneously being charged through a cigarette lighter adapter. The noise goes away when the power line is disconnected. Somehow related to this issue: even when the charging cable is disconnected and the aux input is in use, whenever I change the [automatic] transmission into/from "Parking" mode, the connected phone panics (hangs). It seems as if a surge goes through the AUX line.
Similar threads on this forum [1, 2] suggest ground issues as the possible root cause of these kind of problems. Is there any systematic method to isolate/find the fault?