Yes, I've always had a problem with that scene. First of all, would a firecracker on the balcony really make a sound similar to a gunshot? Secondly, it seems obvious that it would have left traces of the firecracker casing all over the place. Hayward didn't have enough time to wipe it away and still make it back to the room and be in position in time before everyone rushed in. Lastly, that set was so obviously fake - the city scape in the background of the balcony drives me crazy every time I watch it. Couldn't they have filmed that in a real suite? I mean they did it for the Lisa Chambers murder scene in "Double Shock", why not here? Or at least hire someone who could paint something to look real.
Many of the scenes in this were filmed in a studio, which is always a distraction to me. Makes everything look so cheap and staged, rather than natural and interesting to watch.