I was driving the other day and heard a loud pop, and i've never heard a car do that before but I can't seem to find any other way to explain it.

The conditions were unusual: I was driving to a ski resort, so I had been going uphill at slight boost for a few minutes. The temperature was 3 degrees F according to the temp. display. I suddenly hit a fairly steep upward straightaway and decided to gun it, and I was in sports mode at about 4500 rpm when I hear this very loud pop.

Does this sound like a backfire, or should I just assume it was the radio or some other freak occurence? Should i be concerned about it?

For the rest of the night, by the way, whenever the car was at 4500+ rpm at full boost there was a unusual high-pitched sound that almost was like a beep. Since it has gone away, i attribute it to the extreme cold.