After reading these responses, I felt compelled to rate the "winners".
Gold Medal - Goes to the crackling sound of wood. A campfire is the most notable place you might here this, although there are others. The ambiance of crackling wood from a camfire yields one of the most relaxing atmospheres along with the warmth it does provide. I challenge anyone who claims to hate the outdoors, to spend an hour sitting by a campfire and see if their opinion might change.
Silver medal - Goes to the sound of someone else cutting my lawn. I have grown a little to old to enjoy it, and it is a great sound to hear someone else taking my mower for its every five day walk. I can remember times, before the Pittsburgh area somehow moved into the spring and summer monsoon area, where it was only necessary to take my mower for a walk once a month.
Bronze medal - Simply because I am a fisherman myself, is the sound of line being peeled off my reel. Steelhead fishing in the Erie tributaries is a great place to have this happen. That said, the best fight i ever had fresh water fishing was provided by a 30 pound king salmon I caught on Lake Ontario circa 1990. It took just over an hour to land this fish and he made several runs where he peeled more than 300 ft of line off the reel.