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 power 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?

- [1] http://mechanics.stackexchange.com/questions/19752/audio-noise-when-laptop-connected-to-power-inverter-and-the-cars-3-5mm-audio-ja
- [2] http://mechanics.stackexchange.com/questions/8984/series-of-troubling-electrical-problems-in-my-07-mazda-3-any-ideas