Sometimes when in the cargo aircraft during loading they drop a heavy box in the forward door area a couple seconds later the ELEC SMOKE warning comes on with the MASTER WARNING.
Check for electrical fire evidence first! You want to make sure it is really a nuisance and not a real thing. You have time btw. as we are on the ground and all doors open.
You may select OVBD VALVE to OVBD position and wait. Normally it goes away. May be reproduced by jumping up and down again in the door area.
Cause: Dust risen by the falling parcel or jumping
Solution: MX entrance for cleaning up with vacuum
P.S. I've never seen it been done (cleaning up I mean)