I know on the 1.3,1.7 & 2.0CDTI models you get high pitched pulsing tone when you turn off and remove the key which comes from the fuse box area in the engine bay.
Astra-J 2.0 CDTI S/S
Retrofitted AFL, TPMS, Navi950, BT, DAB, Rear Camera, Infinity sound system, Towbar, Flexfloor & more.
I can do programming and retrofits using genuine GM MDI and Dealer software.