'Electrical wirring sound' from underneath the right side back seat is the fuel pump. It should run for about half a second each time the ignition is switched on then stop. It runs again when the engine is cranked and when it is running. If not, fuel pump relay is faulty. It's a common problem.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)