Bombs, at least modern ones, do not "whistle". The whistling sound that Hollywood associates with dropping bombs, went out with the boxkite-tailed weapons of the Second World War. Witnesses who've been close enough to hear modern weapons dropped (and yet far enough away to have survived), reported that falling bombs made an aerodynamic "rustling" sound, not unlike that of an artillary shell.
Of course, "slick" weapons, such as the old iron bombs dropped by B-52s during the Vietnam war, may have acheived transonic or even supersonic velocities by the time they hit the ground...so one would have heard absolutely nothing, as whatever aerodynamic sounds trailed the falling weapon, would have been overwhelmed by the initial shockwave and reverberations caused by its detonation!
Speaking of Hollywood bomb effects, I always smile when I hear a "down doppler" sound whenever they depict a bomb hitting the ground nearby....I guess most of the Foley artists slept through basic physics in high school One would of course, hear an up doppler as the weapon approached....again, if they'd hear anything at all.