Don't take what you see on the screen too seriously. Producers might have assertive opinions about artistic verities, but don't necessarily have staff that were stupid enough to get close enough to falling bombs to know what they sound like, except perhaps as distant crumps. Their criteria for which sound effcts from their libraries to paste in depend more on what they hope will impress their clients and audiences than combat realities.
Plain vanilla bombs do tend to make sounds of increasing pitch as they fall, though not all bombs are very noisy in flight; it depnds on their streamlining. Some bombs and their bombers, especially dive bombers, actually had whistles or the like attached for purposes of terrifying the troops that they attacked in blitzkrieg for example.
Others, particularly some special purpose modern bombs, deploy air brakes or parachutes, leaving them with not much capacity for song.
Because of their inefficient aerodynamics, shells on the other hand very commonly do slow fairly abruptly as they approach, which makes their tone drop. I haven't heard the approach of modern long-range shells though, so I cannot say what they sound like (any comments, anyone with live experience?)
There may sometimes be confounding factors as projectiles pass one, such as shells passing over, which causes impressive Doppler effects, but of course, bombs seldom pass over to any great extent. Not in free fall, anyway. The typical passing bullet simply makes a cracking sound as it goes by. Ricochets and fragments tend to produce a fading, shriilling noise.
Duck!
Jon
