Man... thats very unusual (to say the very least)... things like this sometimes seems too strange for being just coincidences... well... they may be, and they may be not... maybe there is a scientifical explanation for this... but maybe there is not, and it is something "paranormal"... but even if it were, and even if it were actually caused by "spirits", or whatever be called any non-organic (or even non-physical) beings, i dont think its the "ghost" of your granpa. I believe the spirit of the deceased persons doesnt stay in our physical realm, but goes to other places, and so whoever may be causing this things is not your granpa (or his "ghost", "spirit", etc).