If someone was to take a few inexpert pot-shots at you with a rifle from about 500 yards away, what would you hear? Assume a fairly big cartridge, .308 or 7.62 NATO ball.
Would the bullet still be supersonic after 500 yards? Would you hear a supersonic bullet crack, apparently nearby, and the distant muzzle report a half-second later? Or if the bullet had slowed to subsonic, could you hear it pass?
You can figure that the speed of sound is about 1000 or 1100 feet per second, 340.29 m/s. You can also figure that the muzzle velocity of a 30-06 round is in the area of 2300 f/s and that a NATO round and a .306 or .303 round is about the same. The bullet would not lose all that much speed in the first 1500 feet or so. So, yes, 500 yards down range the bullet would be traveling at supersonic speed.
From experience the sound you would hear as the bullet went past you 500 yards down range would be a “snap.” That noise is the sound wave of the bullet itself, the report of the rifle would follow an instant later. If a bunch of high velocity bullets were coming buy you would be hard pressed to associate and one “snap” with any one report.
Please note, the above is not from being shot at, it is based on pulling targets on a known distance range. Acquaintances who have had the luck to be shot at and missed, or at least not killed, confirm the information, however.
How would you describe the sound of the report itself? Past 30 yards or so, I found handgun fire sounds remarkably like kernels of popping corn in a microvawe bag, only a bit more individually distinct. However, while I have heard a few rifles fired, (mostly in the .223 caliber range) I have never heard anything that starts with a “3”, and certainly nothing from downrange.
In the DVD of Master & Commander, the special features had a featurette where they recorded the sound of a medium/small muzzle loading black powder cannon from the 12 clock directions. It was amazing mow much the sound changed depending on direction. Pitch varied, but you also did or did not get different harmonics.
Nearby rifle fire (to me) sounds like a “throaty” firecracker, or like when you hear someone in your neighborhood hammering a block or two away.
The question actually was incoming rifle fire.
You don’t hear a thing. 
Rifle bullets wizzing by you…that’s already been answered.
Ok, yeah, I get that. We’ve had a few houses around us get new roofs. What you describes sounds a notch or two higher pitched than a shotgun. It would have a bit of an echo-y or “reverb” quality to it, wouldn’t it…
Keep your head down over there, madmonk, you seem to have a knack for " noisy-neighbourhood" postings. (first Baghdad, now this.)