I used to do that too :)....I got in trouble one Christmas in the 80's because I talked my brother into sneaking out to the Christmas tree in the middle of the night and unwrapping the corners of our presents to see what we were getting.  Well, that year I received a Speak & Spell (anyone remember those first Texas Instrument computers?....I think there was one for spelling and one for math).....Anyway, the batteries were already loaded and so it made a very loud and distinct noise when I started messing with it to figure it out.....my present and my presence GOT FOUND OUT.