Well if you asked that to a tennis player the answer will definitely be the sound of ---- opening a new can tennis balls which is only heightened by the anticipation of playing with the fantastically bright and perfectly firm tennis balls :)
On the flip side what is that that you don't want to hear? ... The Snap! the snap of your racket string. The first time it happened I didn't event recognize it and when I did I felt a wee bit proud of myself for having broken my first string and for having played enough to have broken one!
The fancy sure wore off the second time around especially since it was Christmas holidays and I was looking forward to playing tennis with tennis courts available round that the clock and to add to that none of the tennis pros were available to restring my racket. Fortunately for me a kind soul who was still in town agreed to restring my racket if I could bring the racket to his home.